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  • Interfacial Biocatalysis on Charged and Immobilized Substrates: The Roles of Enzyme and Substrate Surface Charge LANGMUIR Feller, B. E., Kellis, J. T., Cascao-Pereira, L. G., Robertson, C. R., Frank, C. W. 2011; 27 (1): 250-263

    Abstract

    An enzyme charge ladder was used to examine the role of electrostatic interactions involved in biocatalysis at the solid-liquid interface. The reactive substrate consisted of an immobilized bovine serum albumin (BSA) multilayer prepared using a layer-by-layer technique. The zeta potential of the BSA substrate and each enzyme variant was measured to determine the absolute charge in solution. Enzyme adsorption and the rate of substrate surface hydrolysis were monitored for the enzyme charge ladder series to provide information regarding the strength of the enzyme-substrate interaction and the rate of interfacial biocatalysis. First, each variant of the charge ladder was examined at pH 8 for various solution ionic strengths. We found that for positively charged variants the adsorption increased with the magnitude of the charge until the surface became saturated. For higher ionic strength solutions, a greater positive enzyme charge was required to induce adsorption. Interestingly, the maximum catalytic rate was not achieved at enzyme saturation but at an invariable intermediate level of adsorption for each ionic strength value. Furthermore, the maximum achievable reaction rate for the charge ladder was larger for higher ionic strength values. We propose that diffusion plays an important role in interfacial biocatalysis, and for strong enzyme-substrate interaction, the rate of diffusion is reduced, leading to a decrease in the overall reaction rate. We investigated the effect of substrate charge by varying the solution pH from 6.1 to 8.7 and by examining multiple ionic strength values for each pH. The same intermediate level of adsorption was found to maximize the overall reaction rate. However, the ionic strength response of the maximum achievable rate was clearly dependent on the pH of the experiment. We propose that this observation is not a direct effect of pH but is caused by the change in substrate surface charge induced by changing the pH. To prove this hypothesis, BSA substrates were chemically modified to reduce the magnitude of the negative charge at pH 8. Chemical modification was accomplished by the amidation of aspartic and glutamic acids to asparagine and glutamine. The ionic strength response of the chemically modified substrate was considerably different than that for the native BSA substrate at an identical pH, consistent with the trend based on substrate surface charge. Consequently, for substrates with a low net surface charge, the maximum achievable catalytic rate of the charge ladder was relatively independent of the solution ionic strength over the range examined; however, at high net substrate surface charge, the maximum rate showed a considerable ionic strength dependence.

    View details for DOI 10.1021/la103079t

    View details for Web of Science ID 000285560400034

    View details for PubMedID 21128607

  • The Role of Electrostatic Interactions in Protease Surface Diffusion and the Consequence for Interfacial Biocatalysis LANGMUIR Feller, B. E., Kellis, J. T., Cascao-Pereira, L. G., Robertson, C. R., Frank, C. W. 2010; 26 (24): 18916-18925

    Abstract

    This study examines the influence of electrostatic interactions on enzyme surface diffusion and the contribution of diffusion to interfacial biocatalysis. Surface diffusion, adsorption, and reaction were investigated on an immobilized bovine serum albumin (BSA) multilayer substrate over a range of solution ionic strength values. Interfacial charge of the enzyme and substrate surface was maintained by performing the measurements at a fixed pH; therefore, electrostatic interactions were manipulated by changing the ionic strength. The interfacial processes were investigated using a combination of techniques: fluorescence recovery after photobleaching, surface plasmon resonance, and surface plasmon fluorescence spectroscopy. We used an enzyme charge ladder with a net charge ranging from -2 to +4 with respect to the parent to systematically probe the contribution of electrostatics in interfacial enzyme biocatalysis on a charged substrate. The correlation between reaction rate and adsorption was determined for each charge variant within the ladder, each of which displayed a maximum rate at an intermediate surface concentration. Both the maximum reaction rate and adsorption value at which this maximum rate occurs increased in magnitude for the more positive variants. In addition, the specific enzyme activity increased as the level of adsorption decreased, and for the lowest adsorption values, the specific enzyme activity was enhanced compared to the trend at higher surface concentrations. At a fixed level of adsorption, the specific enzyme activity increased with positive enzyme charge; however, this effect offers diminishing returns as the enzyme becomes more highly charged. We examined the effect of electrostatic interactions on surface diffusion. As the binding affinity was reduced by increasing the solution ionic strength, thus weakening electrostatic interaction, the rate of surface diffusion increased considerably. The enhancement in specific activity achieved at the lowest adsorption values is explained by the substantial rise in surface diffusion at high ionic strength due to decreased interactions with the surface. Overall, knowledge of the electrostatic interactions can be used to control surface parameters such as surface concentration and surface diffusion, which intimately correlate with surface biocatalysis. We propose that the maximum reaction rate results from a balance between adsorption and surface diffusion. The above finding suggests enzyme engineering and process design strategies for improving interfacial biocatalysis in industrial, pharmaceutical, and food applications.

    View details for DOI 10.1021/la103080a

    View details for Web of Science ID 000285217700047

    View details for PubMedID 21080656

  • Open Doorway to Truth: Legacy of the Minnesota Tobacco Trial MAYO CLINIC PROCEEDINGS Hurt, R. D., Ebbert, J. O., Muggli, M. E., Lockhart, N. J., Robertson, C. R. 2009; 84 (5): 446-456

    Abstract

    More than a decade has passed since the conclusion of the Minnesota tobacco trial and the signing of the Master Settlement Agreement (MSA) by 46 US State Attorneys General and the US tobacco industry. The Minnesota settlement exposed the tobacco industry's long history of deceptive marketing, advertising, and research and ultimately forced the industry to change its business practices. The provisions for public document disclosure that were included in the Minnesota settlement and the MSA have resulted in the release of approximately 70 million pages of documents and nearly 20,000 other media materials. No comparable dynamic, voluminous, and contemporaneous document archive exists. Only a few single events in the history of public health have had as dramatic an effect on tobacco control as the public release of the tobacco industry's previously secret internal documents. This review highlights the genesis of the release of these documents, the history of the document depositories created by the Minnesota settlement, the scientific and policy output based on the documents, and the use of the documents in furthering global public health strategies.

    View details for Web of Science ID 000265618000009

    View details for PubMedID 19411441

  • Enzymatic Proteolysis of a Surface-Bound alpha-Helical Polypeptide LANGMUIR Hardesty, J. O., Cascao-Pereira, L., Kellis, J. T., Robertson, C. R., Frank, C. W. 2008; 24 (24): 13944-13956

    Abstract

    In this work, we studied the interactions of enzymes with model substrate surfaces using label-free techniques. Our model system was based on serine proteases (a class of enzymes that digests proteins) and surface-bound polypeptide substrates. While previous studies have focused on bulk media factors such as pH, ionic strength, and surfactants, this study focuses on the role of the surface-bound substrate itself. In particular, we assess how the substrate density of a polypeptide with an alpha-helical secondary structure influences surface reactivity. An alpha-helical secondary structure was chosen based on literature indicating that stable alpha-helices can resist enzymatic digestion. To investigate the protease resistance of a surface-bound a-helix, we designed an a-helical polypeptide (SS-polypeptide, where SS = disulfide), used it to form films of varying surface coverage and then measured responses of the films to enzymatic exposure. Using quartz-crystal microbalance with dissipation (QCM-D), angle-resolved X-ray photoelectron spectroscopy (AR-XPS), grazing-angle infrared spectroscopy (GAIRS), and other techniques, we characterized the degradation of films to determine how the lateral packing density of the surface-bound SS-polypeptide substrate affected surface proteolysis. Characterization of pure SS-polypeptide films indicated dense packing of helices that maintained their helical structure and were generally oriented normal to the surface. We found that films of pure SS-polypeptide significantly resisted enzymatic digestion, while incorporation of very minor amounts of a diluent in such films resulted in rapid digestion. In part, this may be due to the need for the enzyme to bind several peptides along the peptide substrate within the cleft for digestion to occur. Only SS-polypeptide films that were densely packed and did not permit catalytic access to multiple peptides (e.g., terminal peptides only) were resistant to enzymatic proteolysis.

    View details for DOI 10.1021/la8020386

    View details for Web of Science ID 000261631700022

    View details for PubMedID 19360953

  • Fluorescence Quantification for Surface Plasmon Excitation LANGMUIR Feller, B. E., Kellis, J. T., Cascao-Pereira, L. G., Knoll, W., Robertson, C. R., Frank, C. W. 2008; 24 (21): 12303-12311

    Abstract

    Surface plasmon resonance and surface plasmon fluorescence spectroscopy in combination have the potential to distinguish multicomponent surface processes. However, surface intensity variations from resonance angle shifts lead to a nonlinear response in the fluorescence intensity. We report a method to account for surface intensity variations using the experimentally measured relationship between fluorescence and reflectivity. We apply this method to monitor protease adsorption and proteolytic substrate degradation simultaneously. Multilayer protein substrates are prepared for these degradation studies using a layer-by-layer technique.

    View details for Web of Science ID 000260508800034

    View details for PubMedID 18844383

  • Waking a sleeping giant: The tobacco industry's response to the polonium-210 issue AMERICAN JOURNAL OF PUBLIC HEALTH Muggli, M. E., Ebbert, J. O., Robertson, C., Hurt, R. D. 2008; 98 (9): 1643-1650

    Abstract

    The major tobacco manufacturers discovered that polonium was part of tobacco and tobacco smoke more than 40 years ago and attempted, but failed, to remove this radioactive substance from their products. Internal tobacco industry documents reveal that the companies suppressed publication of their own internal research to avoid heightening the public's awareness of radioactivity in cigarettes. Tobacco companies continue to minimize their knowledge about polonium-210 in cigarettes in smoking and health litigation. Cigarette packs should carry a radiation-exposure warning label.

    View details for DOI 10.2105/AJPH.2007.130963

    View details for Web of Science ID 000258476400026

    View details for PubMedID 18633078

  • Downloadable computer models for renal replacement therapy KIDNEY INTERNATIONAL Walther, J. L., Bartlett, D. W., Chew, W., Robertson, C. R., Hostetter, T. H., Meyer, T. W. 2006; 69 (6): 1056-1063

    Abstract

    Mathematical models can predict solute clearances and solute concentrations during renal replacement therapy. At present, however, most nephrologists cannot use these models because they require mathematical software. In this report, we describe models of solute transport by convection and diffusion adapted to run on the commonly available software program Excel for Macintosh computers and PCs running Windows. Two programs have been created that can be downloaded from http://www.stanford.edu/~twmeyer/ or http://dev.satellitehealth.com/research/journal.asp. The first, called 'Dr Addis Clearance Calculator', calculates clearance values from inputs including the blood flow Q(b), the hematocrit, the ultrafiltration rate Q(f), the dialysate flow rate Q(d), the reflection coefficient sigma and the mass transfer area coefficient K(o)A for the solute of interest, and the free fraction f if the solute is protein bound. Solute concentration profiles along the length of the artificial kidney are displayed graphically. The second program, called 'Dr Coplon Dialysis Simulator', calculates plasma solute concentrations from the clearance values obtained by the first program and from additional input values including the number of treatments per week, the duration of the treatments, and the solute's production rate and volumes of distribution. The program calculates the time-averaged solute concentration and provides a graphic display of the solute concentration profile through a week-long interval.

    View details for DOI 10.1038/sj.ki.5000196

    View details for Web of Science ID 000236340100020

    View details for PubMedID 16528255

  • Simultaneous observation of enzyme surface diffusion and surface reaction using microfluidic patterning of substrate surfaces ANALYTICAL CHEMISTRY Roy, S., Thomas, J. M., Holmes, E. A., KELLIS, J. T., Poulose, A. J., Robertson, C. R., Gast, A. P. 2005; 77 (24): 8146-8150

    Abstract

    We present a study of the simultaneous observation of protease reaction and surface diffusion as the enzyme interacts with a model substrate surface. We use micro-fluidic patterning to decorate a bovine serum albumin substrate surface with stripes of adsorbed enzyme in the absence of physical barriers. Spreading of the enzyme from the initial striped region indicates surface diffusion, while removal of the substrate provides a measure of reactivity. Microfluidic patterning provides a means to determine the relative importance of enzyme adsorption, surface diffusion, and reaction on the rate of substrate removal.

    View details for DOI 10.1021/ac050544p

    View details for Web of Science ID 000234079200039

    View details for PubMedID 16351167

  • The clearance of protein-bound solutes by hemofiltration and hemodiafiltration KIDNEY INTERNATIONAL Meyer, T. W., Walther, J. L., Pagtalunan, M. E., Martinez, A. W., Torkamani, A., Fong, P. D., Recht, N. S., Robertson, C. R., Hostetter, T. H. 2005; 68 (2): 867-877

    Abstract

    Hemofiltration in the form of continuous venovenous hemofiltration (CVVH) is increasingly used to treat acute renal failure. Compared to hemodialysis, hemofiltration provides high clearances for large solutes but its effect on protein-bound solutes has been largely ignored.Standard clinical systems were used to remove test solutes from a reservoir containing artificial plasma. Clearances of the protein-bound solutes phenol red (C(PR)) and indican (C(IN)) were compared to clearances of urea (C(UREA)) during hemofiltration and hemodiafiltration. A mathematical model was developed to predict clearances from values for plasma flow Q(p), dialysate flow Q(d), ultrafiltration rate Q(f), filter size and the extent of solute binding to albumin.When hemofiltration was performed with Q(p) 150 mL/min and Q(f) 17 mL/min, clearance values were C(PR) 1.0 +/- 0.1 mL/min; C(IN) 3.7 +/- 0.5 mL/min; and C(UREA) 14 +/- 1 mL/min. The clearance of the protein-bound solutes was approximately equal to the solute-free fraction multiplied by the ultrafiltration rate corrected for the effect of predilution. Addition of Q(d) 42 mL/min to provide HDF while Q(p) remained 150 mL/min resulted in proportional increases in the clearance of protein-bound solutes and urea. In contrast, the clearance of protein-bound solutes relative to urea increased when hemodiafiltration was performed using a larger filter and increasing Q(d) to 300 mL/min while Q(p) was lowered to 50 mL/min. The pattern of observed results was accurately predicted by mathematical modeling.In vitro measurements and mathematical modeling indicate that CVVH provides very limited clearance of protein-bound solutes. Continuous venous hemodiafiltration (CVVHDF) increases the clearance of protein-bound solutes relative to urea only when dialysate flow rate and filter size are increased above values now commonly employed.

    View details for Web of Science ID 000230342500049

    View details for PubMedID 16014068

  • Helical crystallization on lipid nanotubes: Streptavidin as a model protein JOURNAL OF STRUCTURAL BIOLOGY Dang, T. X., Farah, S. J., Gast, A., Robertson, C., Carragher, B., Egelman, E., Wilson-Kubalek, E. M. 2005; 150 (1): 90-99

    Abstract

    In this study, we use streptavidin (SA) as a model system to study helical protein array formation on lipid nanotubes, an alternative to 2D studies on lipid monolayers. We demonstrate that wild-type and a mutant form of SA form helical arrays on biotinylated lipid nanotubes. 3D maps from helical arrays of wild-type and mutant SA were reconstructed using two different approaches: Fourier-Bessel methods and an iterative single particle algorithm. The maps show that wild-type and mutant streptavidin molecules order differently. The molecular packing arrangements of SA on the surface of the lipid nanotubes differ from previously reported lattice packing of SA on biotinylated monolayers. Helical crystallization on lipid nanotubes presents an alternative platform to explore fundamentals of protein ordering, intermolecular protein interaction and phase behavior. We demonstrate that lipid nanotubes offer a robust and reproducible substrate for forming helical protein arrays which present a means for studying protein structure and structure-function relationships.

    View details for DOI 10.1016/j.jsb.2005.02.002

    View details for Web of Science ID 000228196500009

    View details for PubMedID 15797733

  • Increasing dialysate flow and dialyzer mass transfer area coefficient to increase the clearance of protein-bound solutes JOURNAL OF THE AMERICAN SOCIETY OF NEPHROLOGY Meyer, T. W., Leeper, E. C., Bartlett, D. W., Depner, T. A., Lit, Y. Z., Robertson, C. R., Hostetter, T. H. 2004; 15 (7): 1927-1935

    Abstract

    Clinical hemodialysis systems achieve high single pass extraction of small solutes that are not bound to plasma proteins. But they clear protein-bound solutes much less effectively. This study examines the extent to which clearance of a protein-bound test solute is improved by increasing the dialyzer mass transfer area coefficient (KoA) and the dialysate flow rate (Qd). A reservoir containing test solutes and artificial plasma with albumin concentration approximately 4 g/dl was dialyzed with a standard clinical dialysate delivery system. The clearance of phenol red (ClPR) was compared with the clearances of urea and creatinine at a plasma flow rate (Qp) of 200 ml/min with varying values of KoA and Qd. ClPR increased from 11 +/- 2 ml/min to 23 +/- 2 ml/min when KoA for phenol red, KoAPR, was increased from 238 to 640 ml/min and Qd was increased from 286 +/- 6 ml/min to 734 +/- 9 ml/min. Increasing either KoAPR or Qd alone had lesser effects. Clearance values for phenol red were much lower than clearance values for the unbound solutes urea and creatinine, which ranged from 150 to 200 ml/min and were less affected by varying KoA and Qd. A mathematical model was developed to predict ClPR from values of Qp, Qd, the fraction of phenol red bound to albumin (94% +/- 1%) and KoAPR. The model accurately predicts the pattern of measured results and shows further that ClPR can be made to approach Qp only by very large increases in both KoAPR and Qd.

    View details for DOI 10.1097/01.asn.0000131521.62256.f0

    View details for Web of Science ID 000222275600030

    View details for PubMedID 15213283

  • Surface plasmon resonance/surface plasmon enhanced fluorescence: An optical technique for the detection of multicomponent macromolecular adsorption at the solid/liquid interface LANGMUIR Roy, S., Kim, J. H., KELLIS, J. T., Poulose, A. J., Robertson, C. R., Gast, A. P. 2002; 18 (16): 6319-6323

    View details for DOI 10.1021/la025578w

    View details for Web of Science ID 000177224400055

  • Protease adsorption and reaction on an immobilized substrate surface LANGMUIR Kim, J. H., Roy, S., KELLIS, J. T., Poulose, A. J., Gast, A. P., Robertson, C. R. 2002; 18 (16): 6312-6318

    View details for DOI 10.1021/la025579o

    View details for Web of Science ID 000177224400054

  • Surface shear rheology of a polymerizable lipopolymer monolayer LANGMUIR Brooks, C. F., Thiele, J., Frank, C. W., O'Brien, D. F., Knoll, W., Fuller, G. G., Robertson, C. R. 2002; 18 (6): 2166-2173

    View details for DOI 10.1021/la0112312

    View details for Web of Science ID 000174403000032

  • Point mutagenesis and cocrystallization of wild-type and mutant proteins: A study of solid-phase coexistence in two-dimensional protein arrays LANGMUIR Farah, S. J., Wang, S. W., Chang, W. H., Robertson, C. R., Gast, A. P. 2001; 17 (19): 5731-5735
  • Role of N- and C-terminal amino acids in two-dimensional streptavidin crystal formation LANGMUIR Wang, S. W., Robertson, C., Gast, A., Koppenol, S., Edwards, T., Vogel, V., Stayton, P. 2000; 16 (11): 5199-5204
  • Protease activity on an immobilized substrate modified by polymers: Subtilisin BPN ' LANGMUIR Esker, A. R., Brode, P. F., Rubingh, D. N., Rauch, D. S., Yu, H., Gast, A. P., Robertson, C. R., Trigiante, G. 2000; 16 (5): 2198-2206
  • Two-dimensional streptavidin crystals: macropatterns and micro-organization BIOMOLECULAR ENGINEERING Gast, A. P., Robertson, C. R., Wang, S. W., Yatcilla, M. T. 1999; 16 (1-4): 21-27

    Abstract

    Two dimensional crystals of streptavidin grown on lipid monolayers can be viewed as model systems for the study of phase transitions and morphology. These crystals form a variety of macroscopic morphologies associated with different microscopic crystal structures. Observed morphologies are similar to those found in two-dimensional lipid systems, and growth of the protein arrays is somewhat analogous. Such solid state physical processes as nucleation, transformation between crystal phases, crystal phase coexistence, and roughening have been observed in the streptavidin system. In this review, we highlight observations that cause streptavidin to remain an interesting model system exhibiting a variety of intriguing phenomena.

    View details for Web of Science ID 000085673400005

    View details for PubMedID 10796981

  • Two-dimensional crystallization of streptavidin mutants JOURNAL OF PHYSICAL CHEMISTRY B Wang, S. W., Robertson, C. R., Gast, A. P. 1999; 103 (37): 7751-7761
  • Pseudo first-order cleavage of an immobilized substrate by an enzyme undergoing two-dimensional surface diffusion JOURNAL OF COLLOID AND INTERFACE SCIENCE Trigiante, G., Gast, A. P., Robertson, C. R. 1999; 213 (1): 81-86
  • An interfacial stress rheometer to study rheological transitions in monolayers at the air-water interface LANGMUIR Brooks, C. F., Fuller, G. G., Frank, C. W., Robertson, C. R. 1999; 15 (7): 2450-2459
  • Molecular arrangement in two-dimensional streptavidin crystals LANGMUIR Wang, S. W., Robertson, C. R., Gast, A. P. 1999; 15 (4): 1541-1548
  • Pseudo First-Order Cleavage of an Immobilized Substrate by an Enzyme Undergoing Two-Dimensional Surface Diffusion. Journal of colloid and interface science Trigiante, G., Gast, A. P., Robertson, C. R. 1999; 213 (1): 81-86

    Abstract

    In this paper we study the reaction kinetics of an enzyme adsorbed on a peptide substrate surface. Although the adsorption is effectively irreversible, the enzyme is able to diffuse on the surface. Our reaction system consisted of the enzyme collagenase and the oligopeptide FALGPA, a substrate for the enzyme. A quartz surface was coated with covalently bound substrate molecules. The extent of reaction was monitored continuously in a flow cell via UV absorption. The data are compatible with a kinetic model based on a pseudo first-order diffusion/orientation rate-limiting step followed by a relatively fast chemical cleavage step. This model was validated by examining the pH dependence of the rate constant. Copyright 1999 Academic Press.

    View details for PubMedID 10191009

  • Prying open the door to the tobacco industry's secrets about nicotine - The Minnesota Tobacco Trial JAMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION Hurt, R. D., Robertson, C. R. 1998; 280 (13): 1173-1181

    Abstract

    In 1994 the state of Minnesota filed suit against the tobacco industry. This trial is now history, but its legacy will carry on into the 21st century because of the revelations contained in the millions of pages of previously secret internal tobacco industry documents made public in the trial. In this article, we review representative documents relating to nicotine addiction, low-tar, low-nicotine cigarettes, and cigarette design and nicotine manipulation in cigarette manufacture. These documents reveal that for decades, the industry knew and internally acknowledged that nicotine is an addictive drug and cigarettes are the ultimate nicotine delivery device; that nicotine addiction can be perpetuated and even enhanced through cigarette design alterations and manipulations; and that "health-conscious" smokers could be captured by low-tar, low-nicotine products, all the while ensuring the marketplace viability of their products. Appreciation of tobacco industry strategies over the past decades is essential to formulate an appropriate legislative and public policy response. We propose key elements for such legislation and urge no legal or financial immunity for the tobacco industry.

    View details for Web of Science ID 000076210800032

    View details for PubMedID 9777818

  • Orientation in a fatty acid monolayer: Effect of flow type LANGMUIR Maruyama, T., Lauger, J., Fuller, G. G., Frank, C. W., Robertson, C. R. 1998; 14 (7): 1836-1845
  • Influence of pH on two-dimensional streptavidin crystals LANGMUIR Yatcilla, M. T., Robertson, C. R., Gast, A. P. 1998; 14 (2): 497-503
  • Deformation and relaxation processes of mono- and bilayer domains of liquid crystalline Langmuir films on water LANGMUIR Lauger, J., Robertson, C. R., Frank, C. W., Fuller, G. G. 1996; 12 (23): 5630-5635
  • Flow-induced molecular orientation of a Langmuir film SCIENCE Maruyama, T., Fuller, G., Frank, C., Robertson, C. 1996; 274 (5285): 233-235
  • Direct visualization of flow-induced anisotropy in a fatty acid monolayer LANGMUIR FRIEDENBERG, M. C., Fuller, G. G., Frank, C. W., Robertson, C. R. 1996; 12 (6): 1594-1599
  • In situ optical studies of flow-induced orientation in a two-dimensional polymer solution MACROMOLECULES FRIEDENBERG, M. C., Fuller, G. G., Frank, C. W., Robertson, C. R. 1996; 29 (2): 705-712
  • ENZYMES ON IMMOBILIZED SUBSTRATE SURFACES - REACTION JOURNAL OF COLLOID AND INTERFACE SCIENCE GASPERS, P. B., Gast, A. P., Robertson, C. R. 1995; 172 (2): 518-529
  • ABSORPTION-SPECTRA INDICATE CONFORMATIONAL ALTERATION OF MYOGLOBIN ADSORBED ON POLYDIMETHYLSILOXANE BIOPHYSICAL JOURNAL Anderson, A. B., Robertson, C. R. 1995; 68 (5): 2091-2097

    Abstract

    To assess the effects of adsorption on protein structure, ultraviolet optical absorption spectra of myoglobin (Mb) bound to polydimethylsiloxane (PDMS) were measured. A flow cell, which enabled adsorption under controlled hydrodynamic conditions, was used in conjunction with a conventional spectrophotometer to obtain the spectra. Adsorption to PDMS reduced significantly the absorbance in the Soret region of the Mb spectrum, whereas the spectrum in the region near 280 nm was essentially unaffected. This result showed that disruption of the native structure of Mb occurs following interaction with PDMS. Furthermore, the change in the absorption spectrum may indicate loss of heme from the heme pocket of the adsorbed protein. Mb structure was altered from its solution configuration within fifteen min of contact with the surface. Exchange of adsorbed Mb with Mb in solution had little or no effect on the absorption spectrum of the surface-confined protein, indicating that exchange occurs only between conformationally altered species or between native species.

    View details for Web of Science ID A1995RH65800049

    View details for PubMedID 7612852

  • ENZYMES ON IMMOBILIZED SUBSTRATE SURFACES - DIFFUSION LANGMUIR GASPERS, P. B., Robertson, C. R., Gast, A. P. 1994; 10 (8): 2699-2704
  • FORMATION OF BILAYER DISKS AND 2-DIMENSIONAL FOAMS ON A COLLAPSING EXPANDING LIQUID-CRYSTAL MONOLAYER LANGMUIR FRIEDENBERG, M. C., Fuller, G. G., Frank, C. W., Robertson, C. R. 1994; 10 (4): 1251-1256
  • MOLECULAR ANALYSIS OF 2-DIMENSIONAL PROTEIN CRYSTALLIZATION JOURNAL OF PHYSICAL CHEMISTRY Ku, A. C., Darst, S. A., Robertson, C. R., Gast, A. P., Kornberg, R. D. 1993; 97 (12): 3013-3016
  • USE OF GLUCOSE STARVATION TO LIMIT GROWTH AND INDUCE PROTEIN-PRODUCTION IN ESCHERICHIA-COLI BIOTECHNOLOGY AND BIOENGINEERING TUNNER, J. R., Robertson, C. R., Schippa, S., Matin, A. 1992; 40 (2): 271-279

    Abstract

    The use of glucose starvation to uncouple the production of recombinant beta-galactosidase from cell growth in Escherichia coli was investigated. A lacZ operon fusion to the carbon starvation-inducible cst-1 locus was used to control beta-galactosidase synthesis. beta-Galactosidase induction was observed only under aerobic starvation conditions, and its expression continued for 6 h following the onset of glucose starvation. The cessation of beta-galactosidase expression closely correlated with the exhaustion of acetate, an overflow metabolite of glucose, from the culture medium. Our results suggest the primary role of acetate in cst-1-controlled protein expression is that of an energy source. Using this information, we metered acetate to a glucose-starved culture and produced a metabolically sluggish state, where growth was limited to a low linear rate and production of recombinant beta-galactosidase occurred continuously throughout the experiment. The cst-1 controlled beta-galactosidase synthesis was also induced at low dilution rates in a glucose-limited chemostat, suggesting possible applications to high-density cell systems such as glucose-limited recycle reactors. This work demonstrates that by using an appropriate promoter system and nutrient limitation, growth can be restrained while recombinant protein production is induced and maintained.

    View details for Web of Science ID A1992HX27500010

    View details for PubMedID 18601113

  • PHYSIOLOGICAL AND GENETIC STRATEGIES FOR ENHANCED SUBTILISIN PRODUCTION BY BACILLUS-SUBTILIS BIOTECHNOLOGY PROGRESS Pierce, J. A., Robertson, C. R., Leighton, T. J. 1992; 8 (3): 211-218

    Abstract

    Defined minimal media conditions were used to assess and subsequently enhance the production of subtilisin by genetically characterized Bacillus subtilis strains. Subtilisin production was initiated by the exhaustion or limitation of ammonium in batch and fed-batch cultures. Expression of the subtilisin gene (aprE) was monitored with a chromosomal aprE::lacZ gene fusion. The beta-galactosidase production driven by this fusion reflected subtilisin accumulation in the culture medium. Subtilisin gene expression was temporally extended in sporulation-deficient strains (spoIIG), relative to co-genic sporogenous strains, resulting in enhanced subtilisin production. Ammonium exhaustion not only triggered subtilisin production in asporogenous spoIIG mutants but also shifted carbon metabolism from acetate production to acetate uptake and resulted in the formation of multiple septa in a significant fraction of the cell population. Fed-batch culture techniques, employing the spoIIG strain, were investigated as a means to further extend subtilisin production. The constant provision of ammonium resulted in linear growth, with doubling times of 11 and 36 h in each of two independent experiments. At the lower growth rate, the responses elicited (subtilisin production, glucose metabolism, and morphological changes) during the feeding regime closely approximated the ammonium starvation response, while at the higher growth rate a partial starvation response was observed.

    View details for Web of Science ID A1992HZ24300007

    View details for PubMedID 1368258

  • MANIPULATION OF HYDROPHOBIC INTERACTIONS IN PROTEIN ADSORPTION LANGMUIR Tilton, R. D., Robertson, C. R., Gast, A. P. 1991; 7 (11): 2710-2718
  • PERFORMANCE OF THE POLYPROPYLENE FIBER TAILSTRING ON THE COPPER-7 INTRAUTERINE-DEVICE JOURNAL OF APPLIED BIOMATERIALS Warner, M. S., MATSUNO, S. J., VIRGIN, C. J., MASTERSON, K. B., Schneider, G. A., Wright, T. E., Robertson, C. R., FIVESTAYLOR, P. 1991; 2 (2): 73-94

    Abstract

    New and used polypropylene tailstrings from the Copper 7 (Cu-7) intrauterine device were examined by a combination of analytical techniques. Optical microscopy, scanning acoustic and electron microscopy, x-ray diffraction, energy dispersive x-ray analysis, and chemical etching were employed to elucidate both the surface and interior morphology of new Cu-7 tailstrings. Tailstrings removed from women following varying periods of use were investigated with optical microscopy, scanning and transmission electron microscopy. In addition, a subset of the used tailstrings were cultured to identify the types of microorganisms associated with them. Our findings show that unused Cu-7 tailstrings are in various stages of degradation owing to a combination of factors which include the high-draw ratio employed during manufacturing, the method of packaging, and the use of a particulate colourant. Furthermore, it is evident that used Cu-7 tailstrings undergo major deterioration while in situ because of the unfavorable interactions between the highly drawn polypropylene and the physiological environment. These results indicate that the polypropylene tailstrings as manufactured for use with the Cu-7 IUD fail to meet accepted design criteria for biomedical implants.

    View details for Web of Science ID A1991FN00300002

    View details for PubMedID 10149078

  • CHARACTERIZATION OF IMMOBILIZED CELL-GROWTH RATES USING AUTORADIOGRAPHY BIOTECHNOLOGY AND BIOENGINEERING Stewart, P. S., KAREL, S. F., Robertson, C. R. 1991; 37 (9): 824-833

    Abstract

    The growth of immobilized Escherichia coli was analyzed by pulse-chase radioisotope labeling of the cell mass with (35)SO(4) (2-) and subsequent liquid emulsion autoradiography of thin cross sections of the cell aggregate. Bacteria were retained in a planar aggregate on a microporous membrane and grown anaerobically on a phosphate-buffered medium with glucose as the sole carbon and energy source. A mathematical model of immobilized cell growth and convection was used to predict the distribution of label in the cell mass and permit information about both the magnitude and variation in the intrinsic growth rate to be extracted. Growing zone dimensions ranging from 4 to 48 mum and growth rates from 0.28 to 0.5 h(-1) were found. Data collected at low glucose concentrations were consistent with a zero-order description of intrinsic growth kinetics. At high glucose concentrations, conditions under which the system was subject to significant pH inhibition, the data were best described by the prediction of a first-order kinetic model. When coupled with a suitable analytical framework, the combination of radioisotope labeling and autoradiography provides a general method for characterizing immobilized cell growth rates.

    View details for Web of Science ID A1991FC90500005

    View details for PubMedID 18600682

  • HYDRAULIC PERMEABILITY OF IMMOBILIZED BACTERIAL-CELL AGGREGATES APPLIED AND ENVIRONMENTAL MICROBIOLOGY FOWLER, J. D., Robertson, C. R. 1991; 57 (1): 102-113

    Abstract

    A dense aggregate of cells was retained in a reactor by a supported porous membrane. A continuous flow of nutrient medium was maintained through the cell aggregate and membrane. The hydraulic resistance of the cell aggregate was monitored throughout experiments with either growing or chemically cross-linked cells, under conditions of varying flow rates. Digital image analysis was used to characterize the sizes, separations, and orientations of several thousand individual cells in electron micrographs of chemically cross-linked cell aggregates. Two nonlinear phenomena were observed. First, the hydraulic resistance varied in direct relation to and reversibly with flow rate. Second, in constant flow-rate experiments the hydraulic resistance increased with time at a faster rate than could be attributed to cell growth. Both of these phenomena were dependent upon and could be explained by the ability of cells to move with respect to one another, under the influences of Brownian motion and of convection. Such relative motion could allow changes in net alignment of cells in the direction of flow and in the volume fraction of cells in the aggregate. This explanation is consistent with image analysis data. The observed sensitivity of hydraulic resistance to flow rate was inconsistent with a model that assumed elastic deformation of individual cells, and no evidence of cell deformation was found in electron micrographs.

    View details for Web of Science ID A1991ER20600015

    View details for PubMedID 16348387

  • METABOLIC BEHAVIOR OF IMMOBILIZED AGGREGATES OF ESCHERICHIA-COLI UNDER CONDITIONS OF VARYING MECHANICAL-STRESS APPLIED AND ENVIRONMENTAL MICROBIOLOGY FOWLER, J. D., Robertson, C. R. 1991; 57 (1): 93-101

    Abstract

    Experiments were conducted on immobilized aggregates of Escherichia coli cells. Mechanical stress was applied by forcing a convective stream of nutrient medium through the aggregate. It was shown to be possible to maintain uniform exponential growth with this convective supply of nutrients. Analysis of effluent from the system allowed investigation of metabolic responses unambiguously attributable to mechanical stress. A reversible increase in catabolic activity was observed after an increase in mechanical stress. Changes in the level of catabolism were accompanied by an alteration in the total acid yield on glucose and in the spectrum of organic acids produced during glucose fermentation. The behavior observed here was likely due to an osmoregulatory response induced by the mechanically stressed bacteria to counteract changes in shape.

    View details for Web of Science ID A1991ER20600014

    View details for PubMedID 2036025

  • DIFFUSIONAL LIMITATIONS OF IMMOBILIZED ESCHERICHIA-COLI IN HOLLOW-FIBER REACTORS - INFLUENCE ON P-31 NMR-SPECTROSCOPY BIOTECHNOLOGY AND BIOENGINEERING BRIASCO, C. A., KAREL, S. F., Robertson, C. R. 1990; 36 (9): 887-901

    Abstract

    Escherichia coli cells were immobilized and grown in hollow-fiber reactors allowing simultaneous NMR spectroscopy and perfusion with nutrient medium. The extent to which the cells were starved due to inadequate mass transfer was predicted using a mathematical model of reaction and diffusion. Reactors were experimentally characterized using (35)S autoradiography to visualize spatial variations in protein synthesis rates and transmission electron microscopy to indicate spatial variations in cell morphology. Mass transfer limitations in reactors operated at 37 degrees C were shown to be severe, with regions of starved cells occupying up to 80% of the cell-containing region. Phosphorus-31 nuclear magnetic resonance (NMR) spectra of the immobilized, perfused cells revealed abnormally low volume-averaged concentrations of sugar phosphates, NTP, and ratios of NTP/NDP in these reactors. Intracellular pH was also depressed in the cells. In order to overcome mass transfer limitations in the cell layer, the reactor growth temperature was decreased. Sulfur-35 autoradiographs of a reactor operated at 16 degrees C did not indicate the presence of starved cells. The NMR spectra obtained from this reactor showed near-normal intracellular pH, metabolite concentrations, and NTP/NDP ratios. The presence of significant mass transfer limitations in a perfused cell sample during NMR spectroscopy is generally undesirable since the resulting spectra can be ambiguous and difficult to interpret. The strategy adopted in this work, namely estimation of the relative rates of reaction and diffusion in the cell mass and appropriate changes in reactor design and operating parameters, should prove generally applicable for the design of perfused cell samples for NMR spectroscopic experiments.

    View details for Web of Science ID A1990ED68600003

    View details for PubMedID 18597289

  • A HOLLOW-FIBER REACTOR DESIGN FOR NMR-STUDIES OF MICROBIAL-CELLS BIOTECHNOLOGY AND BIOENGINEERING BRIASCO, C. A., Ross, D. A., Robertson, C. R. 1990; 36 (9): 879-886

    Abstract

    A hollow-fiber membrane reactor was designed and constructed to allow perfusion of entrapped, dense Escherichia coli cells with nutrient medium during examination of cell metabolism using nuclear magnetic resonance (NMR) spectroscopy. Phosphorus-31 NMR spectra of the perfused cells included peaks for nucleoside di- and triphosphates, sugar phosphates, and pH-sensitive peaks for inorganic phosphate. The observed intensity of the lumenal inorganic phosphate peak was found to depend on flow rate, ruling out the use of this peak as a concentration reference. Absolute intracellular pH values obtained from NMR measurements were found to be accurate to 0.2 pH units due to uncertainties in intracellular ionic concentrations. Relative pH values, however, were found to be sensitive to cell energetic status. The response of E. coli intracellular pH following a shift to carbon starvation medium was monitored with a resolution of 3 min. Use of a hollow-fiber reactor for cell containment and perfusion during NMR spectroscopy enables metabolic experiments of longer duration and of greater variety than is possible using standard, nonperfused sample tubes.

    View details for Web of Science ID A1990ED68600002

    View details for PubMedID 18597288

  • RENAL MEDULLARY MICROCIRCULATION PHYSIOLOGICAL REVIEWS Pallone, T. L., Robertson, C. R., Jamison, R. L. 1990; 70 (3): 885-920

    View details for Web of Science ID A1990DM42700009

    View details for PubMedID 2194225

  • LATERAL DIFFUSION OF BOVINE SERUM-ALBUMIN ADSORBED AT THE SOLID LIQUID INTERFACE JOURNAL OF COLLOID AND INTERFACE SCIENCE Tilton, R. D., Robertson, C. R., Gast, A. P. 1990; 137 (1): 192-203
  • AUTORADIOGRAPHIC DETERMINATION OF MASS-TRANSFER LIMITATIONS IN IMMOBILIZED CELL REACTORS BIOTECHNOLOGY AND BIOENGINEERING KAREL, S. F., Robertson, C. R. 1989; 34 (3): 320-336

    Abstract

    Pseudomonas putida cells were grown in confined volumes in dual-membrane immobilized cell reactors constructed from microporous polyethylene hollow fibers and silicone rubber tubules as a model system for the study of mass transport in microbial aggregates. Local cell concentrations in the reactors reached 300 g dry mass/L. Pulse-chase radioisotope labeling with (35)SO(4) (2-) was used to estimate the rates of cell mass synthesis and degradation. Sulfur incorporation consistently exceeded sulfur release, implying that the cell mass concentration continually increases. The location and size of the cell growth region was determined using liquid emulsion autoradiography of thin sections prepared from labeled reactors. Cell growth occurs in a region less than 25 mum in depth adjacent to the oxygen supply, and the expansion of the cells caused by cell growth promotes convection of the cell mass into regions of the reactor where starving cells accumulate. The combination of mass-balance and spatial distribution measurements that can be made using radioisotope tracers provides a versatile method for determining metabolic rates and limitations caused by mass transfer in immobilized cell reactors.

    View details for Web of Science ID A1989AA86500006

    View details for PubMedID 18588110

  • CELL MASS SYNTHESIS AND DEGRADATION BY IMMOBILIZED ESCHERICHIA-COLI BIOTECHNOLOGY AND BIOENGINEERING KAREL, S. F., Robertson, C. R. 1989; 34 (3): 337-356

    Abstract

    Escherichia coli K-12 cells were grown in a confined volume using microporous hollow fiber membranes. The local cell concentrations in the reactors were above 400 g dry mass/L, in excess of the predicted limit based on the specific volume of free cells determined by tracer exclusion. Cell mass synthesis and degradation rates in these reactors were measured using radioisotope labeling with (35)S. Net accumulation of cell material persisted at these high cell densities. The rates of substrate uptake and cell growth were predicted from the theory of reaction and diffusion assuming that kinetics of cell metabolism are identical for free-living and immobilized cells. This theory was tested by comparison of overall rates and by the size of the region in which cell growth occurred, measured by autoradiography. A yield coefficient of 4 +/- 1 mol sulfur/mol glucose was measured, in agreement with the value determined for free-living cells in similar conditions. Cell growth occurs in a thin layer (10-30 microm), at a rate similar to the growth rate for free cells. Volume expansion by the cells as a consequence of proliferation induces convection of cell mass out of the growth region into a region of the reactor filled with starving cells, which then accumulate in the reactor. The combination of mass-balance and spatial distribution measurements made possible by the use of radioisotope labeling enables a direct test for mass transfer limitations, the determination of the intrinsic cell kinetics, and noninvasive measurements of cell growth in immobilized cell reactors.

    View details for Web of Science ID A1989AA86500007

    View details for PubMedID 18588111

  • MICROBIAL-GROWTH IN A FIXED VOLUME - STUDIES WITH ENTRAPPED ESCHERICHIA-COLI APPLIED MICROBIOLOGY AND BIOTECHNOLOGY Stewart, P. S., Robertson, C. R. 1989; 30 (1): 34-40
  • EFFECTS OF INTRARENAL ADENOSINE ON RENAL-FUNCTION AND MEDULLARY BLOOD-FLOW IN THE RAT AMERICAN JOURNAL OF PHYSIOLOGY Miyamoto, M., Yagil, Y., Larson, T., Robertson, C., Jamison, R. L. 1988; 255 (6): F1230-F1234

    Abstract

    Adenosine is a potent vasodilator of the systemic circulation. Infusion of adenosine into the aorta causes water and sodium retention and a fall in glomerular filtration rate and renal blood flow. The effect of adenosine on medullary blood flow is unknown. Because systemic vasodilatory effects may confound its renal actions, adenosine was infused into the renal artery of anesthetized Munich-Wistar rats at doses of 2, 6, and 15 micrograms/min. A marked dose-dependent increase in urinary flow and sodium excretion was observed. Inulin and p-aminohippuric acid clearance did not change significantly. Blood flow in vasa recta in the exposed renal papilla, as determined by fluorescence videomicroscopy, increased significantly only with the highest dose of adenosine. In control animals infused with the vehicle only, there was no change in any of the above variables. These results indicate that direct intrarenal infusion of adenosine in the rat increases urinary flow and sodium excretion and at higher doses also increases vasa recta blood flow. The effects on urinary flow and sodium excretion were therefore mediated by a mechanism other than an increase in vasa recta blood flow.

    View details for Web of Science ID A1988R495800096

    View details for PubMedID 3202185

  • PRODUCT INHIBITION OF IMMOBILIZED ESCHERICHIA-COLI ARISING FROM MASS-TRANSFER LIMITATION APPLIED AND ENVIRONMENTAL MICROBIOLOGY Stewart, P. S., Robertson, C. R. 1988; 54 (10): 2464-2471

    Abstract

    Mass transfer-limited removal of metabolic products led to product-inhibited growth of Escherichia coli that was immobilized in a model system. Comparison of the growth kinetics of immobilized and free-living cells revealed no further physiological differences between cells in these two modes of existence beyond those manifested in the local concentrations of substrate and product. Bacteria were retained on a microporous membrane in a dense, planar aggregate and were grown anaerobically on a glucose-based minimal medium. Radioisotope labeling of the immobilized cell mass with 35S was used to determine growth kinetic parameters. Growth rates in the immobilized cell layer were measured by an autoradiographic technique which allowed comparison of the size of the growing region with the rate of cell convection caused by growth. Immobilized cell growth rates and growth yields ranged from near maximal (0.56 h-1 and 39 g of dry cell weight/mol of glucose, respectively) to substantially reduced (0.15 h-1 and 15 g/mol). The depression of these kinetic parameters was attributed to product inhibition arising from mass transfer-limited removal of acidic waste products from the cell mass. A simple one-dimensional reaction-diffusion model, which incorporated data on the product-inhibited growth kinetics of free-living cells collected in a product-limited chemostat, satisfactorily predicted product inhibition of immobilized cell growth.

    View details for Web of Science ID A1988Q418300023

    View details for PubMedID 3060016

  • THE EFFECTIVE DIFFUSIVE PERMEABILITY OF A NONREACTING SOLUTE IN MICROBIAL CELL AGGREGATES BIOTECHNOLOGY AND BIOENGINEERING LIBICKI, S. B., Salmon, P. M., Robertson, C. R. 1988; 32 (1): 68-85

    Abstract

    Aggregates of Escherichia coli confined within hollowfiber reactors were either formed in place by culturing cells within the reactors, or were prepared by injecting a cell suspension that had been concentrated by centrifugation. The effective diffusive permeability of an uncharged nonreacting tracer, nitrous oxide, within the cell aggregates was calculated from measurements of the tracer flux through the aggregates. Estimates of the hydraulic permeability were also obtained for the aggregates that were grown in place. The effective diffusive permeability was found to decrease with increasing cell volume fraction to a value, for aggregates comprising 95% cells, of ca. 30% that obtained for cell-free buffer solution. The dependence on the cell volume fraction was described adequately by the well-known HashinShtrikman bounds for a two-phase medium. The transport properties of aggregates cultivated in place were not significantly different from those of aggregates prepared by centrifugation. Furthermore, the effective diffusive permeabilities of the tracer in aggregates prepared from cells treated with detergent or disrupted by dehydration and grinding differed only slightly from the values obtained for aggregates formed from untreated cells. The results suggest that the method of formation of the cell aggregate and the details of the structure of the cells have little influence on the effective diffusive permeability. These findings should be applicable to the transport of other small uncharged solutes, such as oxygen, that can diffuse through cells. The hydraulic permeability estimates for the aggregates cultured in place were several orders of magnitude larger than the values predicted by a theory formulated with the assumption that the cells are impervious to flow and homogeneously distributed within the aggregates. Two possible reasons for this discrepancy are, first, that there is some flow through the cells themselves, and second, that the cells may form discrete clusters separated by relatively open regions.

    View details for Web of Science ID A1988N644500010

    View details for PubMedID 18584720

  • ADSORPTION OF THE PROTEIN ANTIGEN MYOGLOBIN AFFECTS THE BINDING OF CONFORMATION-SPECIFIC MONOCLONAL-ANTIBODIES BIOPHYSICAL JOURNAL Darst, S. A., Robertson, C. R., Berzofsky, J. A. 1988; 53 (4): 533-539

    Abstract

    Five monoclonal antibodies against sperm whale myoglobin have been used to investigate the physical state of the antigen adsorbed onto a polydimethylsiloxane surface. The binding of each antibody is sensitive to the antigen's conformation in solution while the locations of the antigenic sites on the myoglobin molecule for three of the antibodies have been determined (Berzofsky, J.A., G.K. Buckenmeyer, G. Hicks, F.R.N. Gurd, R.J. Feldmann, and J. Minna. 1982. J. Biol. Chem. 257:3189-3198). The binding of the fluorescein isothiocyanate-labeled IgG and Fab antibodies to previously adsorbed myoglobin has been observed using total internal reflection fluorescence. Three of the antibodies bind specifically to surface-adsorbed myoglobin with affinities at least 50% relative to myoglobin in solution whereas two of the antibodies show affinities for the surface-adsorbed myoglobin diminished by at least two orders of magnitude relative to myoglobin in solution. The specific loss of certain antigenic determinants on the adsorbed myoglobin, coupled with the retention of others, indicates a nonrandom adsorption of the myoglobin molecules.

    View details for Web of Science ID A1988M765200009

    View details for PubMedID 3382711

  • A THEORETICAL INVESTIGATION OF CONVECTIVE-TRANSPORT IN THE HOLLOW-FIBER REACTOR CHEMICAL ENGINEERING COMMUNICATIONS Salmon, P. M., LIBICKI, S. B., Robertson, C. R. 1988; 66: 221-248
  • THE BEHAVIOR OF IMMOBILIZED LIVING CELLS - CHARACTERIZATION USING ISOTOPIC TRACERS ANNALS OF THE NEW YORK ACADEMY OF SCIENCES KAREL, S. F., BRIASCO, C. A., Robertson, C. R. 1987; 506: 84-105

    View details for Web of Science ID A1987R094600006

    View details for PubMedID 3324872

  • EFFECT OF V2-RECEPTOR-MEDIATED CHANGES ON INNER MEDULLARY BLOOD-FLOW INDUCED BY AVP AMERICAN JOURNAL OF PHYSIOLOGY Kiberd, B., Robertson, C. R., Larson, T., Jamison, R. L. 1987; 253 (3): F576-F581

    Abstract

    We have previously shown that arginine vasopressin (AVP) in physiological amounts reduces inner medullary blood flow and that the mechanism of this decrease is at least in part mediated by the vasopressor (V1-receptor) action of AVP. To determine whether the antidiuretic action of AVP (V2-receptor) also contributes to the reduction in inner medullary blood flow, we determined capillary blood flow (QVR) in individual descending vasa recta (DVR) and ascending vasa recta (AVR) using fluorescence videomicroscopy in the exposed renal papilla of the anesthetized rat. Three groups of chronically water-diuretic rats were studied in three consecutive periods: control (period 1), experimental (period 2), and recovery (period 3). Group I rats (designated the AVP group) received AVP, 45 ng X h-1 X kg body wt-1; group II (AVP + V2-inhibitor), AVP plus its specific antidiuretic antagonist d(CH2)5[D-Ile2,Thr4]AVP; and group III (V2-inhibitor), the antagonist alone, respectively, in the experimental period 2. Only group I rats concentrated their urine, urine osmolality (Uosmol) = 499 +/- 48 mosmol/kgH2O, whereas urine remained hypotonic throughout in groups II and III. In group I, QVR in DVR and AVR decreased in period 2; but in groups II and III, QVR tended to increase. These results suggest that the AVP-induced decrease in papillary vasa recta blood flow is in part mediated by its antidiuretic V2-receptor as well as by its vasopressor (V1-receptor). They also suggest that the rate of urinary flow in the medullary collecting ducts is a determinant of inner medullary blood flow.

    View details for Web of Science ID A1987K521200075

    View details for PubMedID 2957929

  • REACTION-RATE CALCULATIONS FOR COSUBSTRATES DIFFUSING INTO CATALYST LAYER FROM OPPOSITE SIDES BIOTECHNOLOGY AND BIOENGINEERING KAREL, S. F., Robertson, C. R. 1987; 30 (3): 427-438

    Abstract

    The effects of diffusion on a reaction taking place in a permeable catalyst are examined theoretically for the case where the reaction has two substrates supplied from opposite sides of a catalytic slab. The solutions of the reaction-diffusion equation for combinations of zeroth-and first-order kinetics are given in terms of an effectiveness factor and a parameter describing the position in the layer where the reaction occurs. In these terms, the results vary only weakly with reaction order. The use of the exact solutions for a reaction that is zeroth order in both sub strates is proposed as a general rule for estimating the reaction rate and the reaction position.

    View details for Web of Science ID A1987J502300013

    View details for PubMedID 18581377

  • BOVINE SERUM-ALBUMIN ADSORPTION AND DESORPTION RATES ON SOLID-SURFACES WITH VARYING SURFACE-PROPERTIES JOURNAL OF COLLOID AND INTERFACE SCIENCE Cheng, Y. L., Darst, S. A., Robertson, C. R. 1987; 118 (1): 212-223
  • EFFECT OF ATRIAL-NATRIURETIC-PEPTIDE ON VASA RECTA BLOOD-FLOW IN THE RAT AMERICAN JOURNAL OF PHYSIOLOGY Kiberd, B. A., Larson, T. S., Robertson, C. R., Jamison, R. L. 1987; 252 (6): F1112-F1117

    Abstract

    To determine whether synthetic atrial natriuretic peptide (ANP) increases renal medullary blood flow and if so whether the increase mediates the diuresis and natriuresis induced by ANP, inner medullary vasa recta blood flow in the exposed left renal papilla of anesthetized Munich Wistar rats weighing between 102 and 161 g was measured by fluorescence videomicroscopy. The rats were maintained in a euvolemic state by the infusion of albumin. Synthetic ANP (Auriculin B) was administered intravenously as 2.5 micrograms/kg body wt prime and as a continuous infusion of 0.2 microgram X min-1 X kg body wt-1 to the experimental group (n = 7). Within 2 min after ANP was given, urine flow and sodium excretion increased (29.4 +/- 3.8 to 50.4 +/- 5.8 microliter X min-1 X kidney wt-1, P less than 0.01, and 3.39 +/- 0.57 to 6.05 +/- 0.95 mueq X min-1 X g kidney wt-1, P less than 0.01, respectively), but vasa recta blood flow in descending (DVR) or ascending (AVR) vasa recta did not change significantly (9.5 +/- 2.3 to 10.0 +/- 2.8 nl/min in DVR and 5.3 +/- 1.0 to 6.1 +/- 1.2 nl/min in AVR). Forty-five minutes after ANP was begun, urine flow and sodium excretion increased further (77.1 +/- 11.1 microliter X min-1 X g kidney wt-1 and 12.0 +/- 2.15 mueq X min-1 X g kidney wt-1, respectively), and by this time vasa recta blood flow had increased significantly to 14.0 +/- 2.6 in DVR, P less than 0.01, and 9.8 +/- 1.2 in AVR, P less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1987H804100074

    View details for PubMedID 2954471

  • A THEORETICAL-ANALYSIS OF A HOLLOW-FIBER REACTOR WITH 2 SUBSTRATES CHEMICAL ENGINEERING JOURNAL AND THE BIOCHEMICAL ENGINEERING JOURNAL Salmon, P. M., Robertson, C. R. 1987; 35 (1): B1-B8
  • MASS-TRANSFER LIMITATIONS IN GEL BEADS CONTAINING GROWING IMMOBILIZED CELLS JOURNAL OF THEORETICAL BIOLOGY Salmon, P. M., Robertson, C. R. 1987; 125 (3): 325-332

    Abstract

    Immobilized-cell aggregates have traditionally been approximated as effective continua within which the catalytic activity of the cells is homogeneously distributed. Chang & Park (1985), however, recently modelled the immobilized cells as discrete inclusions within a support matrix. With some modification, this theory is applicable to the analysis of microbial colonies growing within gel beads, and indicates that predictions obtained using the traditional approach may be significantly in error.

    View details for Web of Science ID A1987G970300008

    View details for PubMedID 3309477

  • THE MEDULLARY MICROCIRCULATION KIDNEY INTERNATIONAL ZIMMERHACKL, B. L., Robertson, C. R., Jamison, R. L. 1987; 31 (2): 641-647

    Abstract

    Like other regional circulations, the medullary circulation supplies oxygen and other primary substrates to the medulla and removes carbon dioxide and other waste metabolites. It also acts as a countercurrent exchanger and simultaneously removes water reabsorbed from the renal tubule to preserve mass balance. Our present understanding of how the medulla serves both these functions at the same time is illustrated in Figure 3. Blood leaves the efferent arteriole with an elevated plasma protein concentration as a consequence of glomerular filtration, and flows down descending vasa recta within a vascular bundle. The increased interstitial osmotic-concentration coupled with a finite capillary reflection coefficient for small solutes causes additional water to be extracted so that at the termination of descending vasa recta, the plasma protein concentration exceeds that in the systemic circulation by approximately twofold. Solute, urea more than sodium chloride, also enters descending vasa recta. As blood flows through the interconnecting capillary plexus and up ascending vasa recta, transcapillary oncotic and osmotic pressure differences combine to cause capillary uptake of fluid. There is also simultaneous loss of urea such that the medullary trapping of urea is very effective. Countercurrent exchange of sodium chloride, however, appears to be less efficient and as a consequence, not only water but sodium chloride is removed from the medulla. Antidiuretic hormone reduces medullary blood flow, both directly by its vasoconstrictor (V1-receptor mediated) effect and indirectly by its antidiuretic (V2-receptor mediated) effects. Prostaglandins are able to enhance medullary blood flow by counteracting vasoconstrictive influences.(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1987F981500020

    View details for PubMedID 3550235

  • MODELS OF THE MEDULLARY MICROCIRCULATION KIDNEY INTERNATIONAL MCNEELY, E. A., Pallone, T. L., Deen, W. M., Robertson, C. R. 1987; 31 (2): 662-667

    View details for Web of Science ID A1987F981500022

    View details for PubMedID 3550237

  • PROTEIN ADSORPTION AT POLYMER SURFACES - A STUDY USING TOTAL INTERNAL-REFLECTION FLUORESCENCE ACS SYMPOSIUM SERIES Anderson, A. B., Darst, S. A., Robertson, C. R. 1987; 343: 306-323
  • MYOGLOBIN ADSORPTION ONTO CROSS-LINKED POLYDIMETHYLSILOXANE JOURNAL OF COLLOID AND INTERFACE SCIENCE Darst, S. A., Robertson, C. R., Berzofsky, J. A. 1986; 111 (2): 466-474
  • MEASUREMENT OF INERT-GAS PERMEABILITIES IN COMPACT BACTERIAL-CELL AGGREGATES USING AN ANNULAR REACTOR ANNALS OF THE NEW YORK ACADEMY OF SCIENCES LIBICKI, S. B., Salmon, P. M., Robertson, C. R. 1986; 469: 145-151
  • THE IMMOBILIZATION OF WHOLE CELLS - ENGINEERING PRINCIPLES CHEMICAL ENGINEERING SCIENCE KAREL, S. F., LIBICKI, S. B., Robertson, C. R. 1985; 40 (8): 1321-1354
  • THE MICROCIRCULATION OF THE RENAL MEDULLA CIRCULATION RESEARCH Zimmerhackl, B., Robertson, C. R., Jamison, R. L. 1985; 57 (5): 657-667

    View details for Web of Science ID A1985AUU9600001

    View details for PubMedID 3902277

  • VIDEOMICROSCOPIC METHOD FOR DIRECT DETERMINATION OF BLOOD-FLOW TO THE PAPILLA OF THE KIDNEY ANNALS OF BIOMEDICAL ENGINEERING Jamison, R. L., Zimmerhackl, B., Robertson, C. R. 1985; 13 (3-4): 273-280

    Abstract

    We adapted the technique of videomicroscopy for direct determination of blood flow in individual capillaries of the papilla of the kidney, the ascending vasa recta (AVR) and descending vasa recta (DVR). The papilla was exposed in anesthetized rats and positioned under a video-camera-microscope and viewed under epiillumination. The intravenous infusion of fluorescein-isothiocyanate (FITC)-labeled gamma globulin was combined with fluorescence microscopy to enhance the contrast among plasma, red blood cells and capillary walls. On the television monitor, the walls were clearly outlined, enabling the measurement of capillary diameter. The velocity of red cells (Vrbc) in individual vasa recta was measured using the dual slit technique. From the videotape recorded microscopic image of a vas rectum, two photometric signals were obtained by integrating the light intensity from two electronic "windows" positioned closely together over the same capillary. Red cell velocity was calculated by dividing the distance between the two windows by the time delay between signals. The delay was determined using analog correlation tracking or digital cross correlation techniques. Single vasa recta blood flow was calculated from capillary diameter, Vrbc, and F (Fahraeus factor), which converts Vrbc to average whole blood velocity, Vblood. In quartz capillaries the same size as vasa recta, the ratio F = Vrbc/Vblood = 1.42 +/- 0.06. Total papillary blood inflow and outflow was calculated by multiplying the total number of DVR or AVR times the mean single capillary blood flow for DVR or AVR, respectively.

    View details for Web of Science ID A1985AMX8400006

    View details for PubMedID 4037456

  • USE OF DIGITAL CROSS-CORRELATION FOR ONLINE DETERMINATION OF SINGLE-VESSEL BLOOD-FLOW IN THE MAMMALIAN KIDNEY MICROVASCULAR RESEARCH Zimmerhackl, B., TINSMAN, J., Jamison, R. L., Robertson, C. R. 1985; 30 (1): 63-74

    Abstract

    The empirical relationship between erythrocyte velocity (Vrbc) and mean blood velocity (Vblood) was studied in quartz capillaries by television microscopy using the dual-slit technique. A newly designed desktop digital on-line cross-correlator was combined with a computer to determine Vrbc. The accuracy of the digital correlator was tested for velocities ranging from 0 to 3 mm/sec and compared with values determined using an analog tracking correlation device. There was good agreement. Small-bore glass tubes with diameters ranging from 12 to 26 micron were perfused with suspensions of erythrocytes having hematocrits between 10 and 37%. The relationship between mean blood velocity and erythrocyte velocity in these quartz tubes was found to be Vblood = 0.88 Vrbc - 0.11, and was independent of diameter and hematocrit within the range investigated. The mean ratio for Vrbc/Vblood was 1.42 +/- 0.06.

    View details for Web of Science ID A1985ALE3700007

    View details for PubMedID 4021838

  • DUAL AEROBIC HOLLOW-FIBER BIOREACTOR FOR CULTIVATION OF STREPTOMYCES-AUREOFACIENS BIOTECHNOLOGY AND BIOENGINEERING Robertson, C. R., Kim, I. H. 1985; 27 (7): 1012-1020

    Abstract

    Streptomyces aureofaciens (ATCC 12416c) was grown in the interstitial region formed by a parallel arrangement of three hollow silicone tubules contained within a microporous polypropylene hollow fiber. Liquid-soluble nutrients were supplied by diffusion across the polypropylene fiber to the interstitial cell-containing region whereas air or oxygen was provided by diffusion from the silicone tubule lumina to the cell mass. In this bioreactor, S. aureofaciens grew to high cell densities (greater than 10(11) cells/cm(3)) and the culture so-obtained continously synthesized the secondary metabolite tetracycline. The volumetric productivity of tetracycline based on the interstitial volume was 90 microg/ml/h and based on the total reactor volume was 5.5 microg/mL/h. The high surface area-to-volume ratio afforded by the cylindrical configuration together with spatially distinct conduits to continuously transport liquids and gases, each of which may be nutrients or products of biosynthesis, to or from a tissuelike cell mass provides an alternative to the conventional air- or oxygen-sparged fermentation vessel. High volumetric reactor productivities may be achieved by virute of the concentrated stationary cell mass and by the appropriate selection of fiber sizes and materials so as to ensure adequate supplies of liquid and gaseous substrates to, as well as removal of metabolites from, most cells in the culture. This reactor topology is quite general and may be adapted to most microbial as well as mammalian and plant cell systems.

    View details for Web of Science ID A1985ALX5000011

    View details for PubMedID 18553771

  • ETHANOL-PRODUCTION BY NITROGEN-DEFICIENT YEAST-CELLS IMMOBILIZED IN A HOLLOW-FIBER MEMBRANE BIOREACTOR APPLIED MICROBIOLOGY AND BIOTECHNOLOGY INLOES, D. S., Michaels, A. S., Robertson, C. R., Matin, A. 1985; 23 (2): 85-91
  • EFFECT OF ARGININE VASOPRESSIN ON RENAL MEDULLARY BLOOD-FLOW - A VIDEOMICROSCOPIC STUDY IN THE RAT JOURNAL OF CLINICAL INVESTIGATION Zimmerhackl, B., Robertson, C. R., Jamison, R. L. 1985; 76 (2): 770-778

    Abstract

    The role of arginine vasopressin (AVP) in the regulation of renal medullary blood flow is uncertain. To determine if AVP has a direct vasoconstrictive action on vasa recta, the effect of AVP on erythrocyte velocity (VRBC), diameter, and blood flow (QVR) in descending vasa recta (DVR) and ascending vasa recta (AVR) was studied in the exposed renal papilla of four groups of chronically water diuretic rats using fluorescence videomicroscopy. There were three periods: control (period 1), experimental (period 2), and recovery (period 3). In periods 1 and 3, all groups received hypotonic saline. In period 2, group I rats (AVP) received AVP (45 ng/h per kg body wt); group II (time) received hypotonic saline alone; group III (AVP plus V1-inhibitor) received AVP plus its vascular antagonist, d(CH2)5Tyr(Me)AVP; and group IV (V1-inhibitor) received the vascular antagonist alone. Another group of rats (group V) was employed to demonstrate that the rise in blood pressure induced by a 3- or 10-ng/kg injection of AVP was virtually abolished by the prior infusion of the V1-inhibitor. The urine of group III as well as group I rats was concentrated (Uosm = 721 +/- 62 H2O vs. 670 +/- 39 mosM/kg), while urine remained dilute in groups II and IV. In period 2, VRBC and QVR in DVR and AVR decreased in group I, did not decrease in group III, and increased in groups II and IV. The vascular antagonist thus completely abolished the AVP-induced decrease in QVR in group III. These findings unequivocally establish that AVP in physiological amounts reduces medullary blood flow, at least in part, by a direct vasoconstrictive action on the medullary microcirculation. They also show that an effect of AVP on medullary blood flow is not necessary for its antidiuretic effect.

    View details for Web of Science ID A1985APT9300051

    View details for PubMedID 4031072

  • FLUID UPTAKE IN THE RENAL PAPILLA BY VASA RECTA ESTIMATED BY 2 METHODS SIMULTANEOUSLY AMERICAN JOURNAL OF PHYSIOLOGY Zimmerhackl, B., Robertson, C. R., Jamison, R. L. 1985; 248 (3): F347-F353

    Abstract

    Fluid uptake by vasa recta was determined by two independent methods, videomicroscopy and the micropuncture technique, in the exposed papilla of nine antidiuretic rats to reconcile differences in values previously obtained by the two techniques. Erythrocyte velocity (Vrbc) and diameter (D) in descending vasa recta (DVR) (n = 22) and ascending vasa recta (AVR) (n = 31) near the "base" of the papilla were measured. Using a conversion function determined in vitro, Vrbc was transformed into mean blood velocity (Vblood). From D and Vblood, mean blood flow (Q) in DVR and AVR was calculated. In DVR, mean Vrbc, D, and Q were 1.06 +/- 0.01 mm/s, 16.3 +/- 0.4 micron, and 10.6 +/- 1.4 nl/min, respectively. In AVR, each corresponding value differed significantly, 0.47 +/- 0.06 mm/s (P less than 0.001), 19.8 +/- 0.8 micron (P less than 0.001), and 5.65 +/- 1.3 nl/min (P less than 0.025), respectively. Blood samples from DVR and AVR were obtained by micropuncture from the same location. Plasma protein concentration (g/dl) was 5.1 +/- 0.6 in DVR, 4.0 +/- 0.4 (P less than 0.05) in AVR, and 3.6 +/- 0.3 (P less than 0.025) in the renal vein. Assuming no net transcapillary loss of protein, total plasma outflow exceeded inflow by 29%, the excess representing fluid uptake; and to reconcile the blood flow and plasma protein concentrations found, functioning AVR should outnumber functioning DVR by a ratio of 2.1-2.4 to 1, depending on local hematocrit. Given the total number of AVR + DVR = 2,944 (at the base), capillary fluid uptake was calculated to range between 1.5 and 2.6 microliter/min.

    View details for Web of Science ID A1985ADR5100037

    View details for PubMedID 3976897

  • PROSTAGLANDIN SYNTHESIS INHIBITORS AND VASA RECTA ERYTHROCYTE VELOCITIES IN THE RAT AMERICAN JOURNAL OF PHYSIOLOGY Lemley, K. V., SCHMITT, S. L., Holliger, C., Dunn, M. J., Robertson, C. R., Jamison, R. L. 1984; 247 (4): F562-F567

    Abstract

    Vasa recta erythrocyte velocities (VRBC) in the exposed renal papilla of anesthetized water-loaded rats were determined before and 60 min after intravenous administration of a prostaglandin synthesis inhibitor (indomethacin, meclofenamate) or the inhibitor vehicle alone. The change in VRBC of ascending and descending vasa recta for the inhibitor group [-17 +/- 5% (SE)] was different from that for controls (+12 +/- 4%, P less than 0.002). Erythrocyte velocities were also determined in vasa recta of antidiuretic rats before and 30 min after administration of indomethacin or vehicle alone. Prostaglandin synthesis inhibition was again associated with a significant decrease in VRBC compared with control (-24 +/- 4% vs. +28 +/- 20%, respectively, P less than 0.025). These findings suggest that prostaglandins play a similar role in regulating blood flow in the renal medulla in water diuresis and antidiuresis.

    View details for Web of Science ID A1984AAJ2100052

    View details for PubMedID 6496683

  • EXAMINATION OF TRANS-EPITHELIAL EXCHANGE OF WATER AND SOLUTE IN THE RAT RENAL PELVIS JOURNAL OF CLINICAL INVESTIGATION Bargman, J., Leonard, S. L., McNeely, E., Robertson, C., Jamison, R. L. 1984; 74 (5): 1860-1870

    Abstract

    Severance of the ureter beyond the renal papilla causes a fall in urinary osmolality, which suggests that exchange of water or solute between urine and renal parenchyma normally occurs in the intact renal pelvis. We examined water and solute flux in the renal pelvis with micropuncture and microcatheterization techniques. Four groups of antidiuretic rats were studied. Group I (n = 17) underwent micropuncture through the intact contracting ureter. Urine samples were obtained at the papillary tip, and in the pelvis beside the base of the extrarenal papilla. Urinary osmolality at the base, 880 +/- 97 mosmol/kg H2O (mean +/- SE), was less than that at the tip, 1,425 +/- 104 mosmol/kg H2O (P less than 0.005). In group II (n = 24), samples were analyzed for inulin and osmolality. In 15 rats (group IIA), comparison was made between base and tip samples. In the other nine animals (group IIB), comparisons were made among base, tip, and bladder samples and urea was also measured. In group II (A and B combined) urine-to-plasma (U/P) osmolality was lower at the base, 4.31 +/- 0.27, than at the tip, 6.08 +/- 0.23 (P less than 0.001), and U/P inulin was lower at the base, 192 +/- 25, than at the tip, 306 +/- 16 (P less than 0.001). In group IIB, the bladder urine had a lower U/P osmolality, 5.27 +/- 0.25, than the tip, 6.01 +/- 0.31 (P less than 0.02). The U/P urea was 59 +/- 10.6 (base), 98 +/- 9.4 (tip) (base vs. tip, P less than 0.05), and 81 +/- 6.5 (bladder, P less than 0.005, compared with tip). In group III (n = 8), samples were obtained by microcatheter from the fornices, the deepest intrarenal extensions of the pelvis, and compared with samples at the tip. Urinary osmolality was lower in the fornix, 646 +/- 106 mosmol/kg H2O, than at the tip, 1,296 +/- 99 mosmol/kg H2O (P less than 0.001). Similarly, U/P inulin was lower in the fornix, 48 +/- 14, than at the tip, 128 +/- 12 (P less than 0.001). The lower U/P inulin in the pelvic urine is the result of either the addition of fluid to the pelvis, or the backleak of inulin across the epithelium lining the pelvis. To verify that the pelvic epithelium was impermeable to inulin, in group IVA (n = 4) the left renal pelvis was superfused with a solution of chemical inulin. Cumulative absorption of inulin from the left kidney was 0.15 +/- 0.08% of that superfused. Using [14C]inulin in group IVB (n= 3), similar results were obtained (0.05 +/- 0.02%). These findings indicate that in the renal pelvis, fluid is added to urine after it emerges from the collecting ducts. We suggest that reflux of hyperosmotic urine over the renal papilla creates a transepithelial gradient for the flux of water into the pelvis. A model that incorporates diffusive and convective forces for water and solute transport is proposed to account for these findings.

    View details for Web of Science ID A1984TS19400035

    View details for PubMedID 6501575

  • NATURE OF THE RENAL INJURY FOLLOWING TOTAL RENAL ISCHEMIA IN MAN JOURNAL OF CLINICAL INVESTIGATION Myers, B. D., Miller, D. C., MEHIGAN, J. T., Olcott, C., GOLBETZ, H., Robertson, C. R., Derby, G., Spencer, R., Friedman, S. 1984; 73 (2): 329-341

    Abstract

    The effects of total renal ischemia (TRI) of 15-87 min duration due to suprarenal clamping of the aorta were studied in 15 mannitol-treated patients undergoing abdominal aortic surgery. 15 patients undergoing similar surgery but requiring only infrarenal clamping served as controls. 1-2 h following TRI, GFR was reduced to only 39% of that in controls, 23 +/- 5 vs. 59 +/- 7 ml/min (P less than 0.001). This could not be ascribed to impaired renal plasma flow (RPF), which was mildly reduced to 331 +/- 71 and was not different from the value in controls, 407 +/- 66 ml/min. However, impaired PAH extraction (43 +/- 7%) and isosthenuria, not present in controls, suggest a primary role for tubular injury in lowering GFR at this time. 24 h following TRI, the GFR remained depressed below controls, 45 +/- 8 vs. 84 +/- 8 ml/min (P less than 0.005), while the transglomerular sieving of neutral dextrans was significantly enhanced (radius interval, 24-40 A). A theoretical analysis of transcapillary solute exchange revealed that these findings could be largely explained by a selective reduction of either RPF (-61%) or of transmembrane hydraulic pressure difference (-18%) below control values. Alternately, a combination of these two factors with changes of smaller magnitude could explain the findings. In contrast, a selective increase in oncotic pressure or decrease of the glomerular ultrafiltration coefficient could be excluded as a cause of hypofiltration 24 h after TRI. These observations lead us to suggest that the transient azotemia observed following TRI is due to a self-limited injury to the nephron that is identical to that seen in overt and sustained forms of acute renal failure.

    View details for Web of Science ID A1984SD74800006

    View details for PubMedID 6421876

  • MECHANISMS OF POLARIZATION AND FOULING OF ULTRAFILTRATION MEMBRANES BY PROTEINS JOURNAL OF MEMBRANE SCIENCE REIHANIAN, H., Robertson, C. R., Michaels, A. S. 1983; 16 (DEC): 237-258
  • PROTEIN ADSORPTION ON CROSSLINKED POLYDIMETHYLSILOXANE USING TOTAL INTERNAL-REFLECTION FLUORESCENCE JOURNAL OF COLLOID AND INTERFACE SCIENCE Lok, B. K., Cheng, Y. L., Robertson, C. R. 1983; 91 (1): 104-116
  • TOTAL INTERNAL-REFLECTION FLUORESCENCE - A TECHNIQUE FOR EXAMINING INTERACTIONS OF MACROMOLECULES WITH SOLID-SURFACES JOURNAL OF COLLOID AND INTERFACE SCIENCE Lok, B. K., Cheng, Y. L., Robertson, C. R. 1983; 91 (1): 87-103
  • HOLLOW-FIBER MEMBRANE BIOREACTORS USING IMMOBILIZED ESCHERICHIA-COLI FOR PROTEIN-SYNTHESIS BIOTECHNOLOGY AND BIOENGINEERING INLOES, D. S., Smith, W. J., Taylor, D. P., Cohen, S. N., Michaels, A. S., Robertson, C. R. 1983; 25 (11): 2653-2681

    Abstract

    Actively growing Escherichia coli C600(pBR322), immobilized within the macroporous matrix of asymmetric-wall hollow-fiber membranes, has been propagated to extremely high densities, typically more than 10(12) cells/mL of accessible void volume, in some regions cells accounting for nearly 100% of the available macrovoid volume forming a tissue-like mass. Production rates of beta-lactamase, an enzyme used as an indicator of the culture's biosynthetic potential, remained at high and relatively stable levels for more than three weeks of continuous operation, and effluent supernatant enzyme activities attained 25% of the accumulated level measured in a 24-h shaker-flask culture. Based on the accessible void volume within the fiber wall, the beta-lactamase productivity was independent of the specific asymmetric membrane used. On a per cell basis, however, cells cultured using hollow-fiber membranes were only 10% as productive as those in the shaker-flask culture, possibly due to the high packing density or culture aging. By contrast, the hollow-fiber bioreactor was 100 times more productive than the shaker-flask culture on a reactor-volume basis, primarily as a consequence of the high cell densities. Reactor productivity was dependent on the number of cells in the reactor, suggesting that reactor performance was kinetically controlled and not mass transport limited.

    View details for Web of Science ID A1983RP65900012

    View details for PubMedID 18548600

  • ETHANOL-PRODUCTION BY SACCHAROMYCES-CEREVISIAE IMMOBILIZED IN HOLLOW-FIBER MEMBRANE BIOREACTORS APPLIED AND ENVIRONMENTAL MICROBIOLOGY INLOES, D. S., Taylor, D. P., Cohen, S. N., Michaels, A. S., Robertson, C. R. 1983; 46 (1): 264-278

    Abstract

    Saccharomyces cerevisiae ATCC 4126 was grown within the macroporous matrix of asymmetric-walled polysulfone hollow-fiber membranes and on the exterior surfaces of isotropic-walled polypropylene hollow-fiber membranes. Nutrients were supplied and products were removed by single-pass perfusion of the fiber lumens. Growth of yeast cells within the macrovoids of the asymmetric-walled membranes attained densities of greater than 10 cells per ml and in some regions accounted for nearly 100% of the available macrovoid volume, forming a tissue-like mass. A radial distribution of cell packing existed across the fiber wall, indicating an inadequate glucose supply to cells located beyond 100 mum from the lumen surface. By comparison, yeast cell growth on the exterior surfaces of the isotropic-walled membranes resulted in an average density of 3.5 x 10 viable cells per ml. Ethanol production by reactors containing isotropic polypropylene fibers reached a maximum value of 26 g/liter-h based on the total reactor volume. Reactor performance depended on the fiber packing density and on the glucose medium flow rate and was limited by low nutrient and product transport rates. The inhibition of ethanol production and the reduction in fermentation efficiency arose primarily from the accumulation of CO(2) gas within the sealed reactor shell space.

    View details for Web of Science ID A1983QY25700042

    View details for PubMedID 16346346

  • DIRECT DETERMINATION OF VASA RECTA BLOOD-FLOW IN THE RAT RENAL PAPILLA CIRCULATION RESEARCH Holliger, C., Lemley, K. V., SCHMITT, S. L., Thomas, F. C., Robertson, C. R., Jamison, R. L. 1983; 53 (3): 401-413

    Abstract

    Blood flow in vasa recta capillaries of the exposed renal papilla of young antidiuretic rats (n = 18) was determined by an adaptation of the video-photometric technique of Intaglietta. The erythrocyte velocity and capillary diameter in vasa recta (n = 97) were measured at the same location by means of fluorescence video microscopy, with fluorescein-labeled bovine gamma-globulin as a plasma marker. A factor relating erythrocyte velocity to mean cross-sectional blood velocity was determined in vitro to permit the calculation of single vasa recta blood flows from the measured indices, erythrocyte velocity and capillary diameter. Mean blood flow in descending vasa recta was 8.83 +/- 0.96 (SE) nl/min, significantly greater than that in ascending vasa recta, 4.82 +/- 0.34 nl/min. The total numbers of ascending and descending vasa recta at the base of the exposed papilla were also determined. Over 1500 vasa recta were identified as ascending vasa recta or descending vasa recta in electron micrographs of three papillas. At this level in the papilla (2 mm from the tip), there were four ascending vasa recta for each descending vas rectum. From the total numbers of ascending vasa recta and descending vas rectum, single vessel blood flows were converted to total blood flow. Total blood outflow in all ascending vasa recta, 11.3 microliter/min, substantially exceeded total blood inflow in all descending vasa recta, 5.2 microliter/min. The difference between outflow and inflow (6.1 microliter/min) represents an estimate of water by the papillary microcirculation, and is more than adequate to accommodate the known rate of water reabsorption from the collecting ducts of the exposed papilla.

    View details for Web of Science ID A1983RH49300012

    View details for PubMedID 6883657

  • THEORETICAL-ANALYSIS OF ELECTROSTATIC EFFECTS ON ION-TRANSPORT IN ULTRATHIN MEMBRANES JOURNAL OF THE ELECTROCHEMICAL SOCIETY Bradshaw, R. W., Robertson, C. R. 1982; 129 (5): 958-962
  • THE NATURE OF THE GLOMERULAR INJURY IN MINIMAL CHANGE AND FOCAL SCLEROSING GLOMERULOPATHIES AMERICAN JOURNAL OF KIDNEY DISEASES WINETZ, J. A., Robertson, C. R., GOLBETZ, H. V., Carrie, B. J., SALYER, W. R., Myers, B. D. 1981; 1 (2): 91-98

    Abstract

    Glomerular barrier function was evaluated in 12 healthy human volunteers and in 16 proteinuric patients in whom the nephrotic syndrome was associated with alteration of glomerular epithelial cells alone (minimal change nephropathy [MCN]) or in combination with focal glomerular sclerosis (FGS). We determined the glomerular sieving coefficient for each of nine narrow dextran fractions (Einstein Stoke radius [ESR] = 30 to 46 A), and directly measured, or indirectly estimated, values for the determinants of glomerular ultrafiltration. These quantities were then subjected to analysis based on an hydrodynamic theory of solute transport through an isoporous membrane. The results indicate that relative to normal subjects, effective pore radius is reduced from 59 to 55 and 53 A in McN and FGS, respectively; while the ratio, pore area to pore length (a measure of pore density) is correspondingly reduced from 21.7 X 10(6) to 10.1 X 10(6) and 4.7 X 10(6) cm. respectively, We suggest that collapse of the anionic glomerular membrane matrix in these proteinuric disorders may lead to pore shrinkage and reduced pore density, but that reduced electrostatic repulsion of anionic albumin (ESR = 36 A) facilitates its permeation into Bowman's space. The qualitatively similar disorder of glomerular barrier function in MCN and FGS is consistent with a unitary pathogenesis, but may represent a nonspecific response to depletion of glomerular polyanion.

    View details for Web of Science ID A1981MP41200004

    View details for PubMedID 6174043

  • DYNAMICS OF GLOMERULAR ULTRAFILTRATION FOLLOWING OPEN-HEART SURGERY KIDNEY INTERNATIONAL Myers, B. D., Hilberman, M., Carrie, B. J., Spencer, R. J., Stinson, E. B., Robertson, C. R. 1981; 20 (3): 366-374

    Abstract

    To elucidate how individual determinants might lower the rate of glomerular ultrafiltration (GFR) in some patients following cardiac surgery, we performed hemodynamic measurements and clearance of inulin (as a measure of GFR), PAH (as a measure of effective renal plasma flow [ERPF]), and dextran-40. Two groups of 17 patients each were distinguished by the presence or absence of prerenal azotemia. Glomerular hypofiltration (GFR = 21 +/- 2 vs. 76 +/- 6 ml/min/1.73 m2, P less than 0.001) in the former was accompanied by depressed left ventricular function, arterial pressure, and ERPF (152 +/- 26 vs. 317 +/- 32 ml/min/1.73 m2, P less than 0.001). To determine if factors beside ERPF play a role in lowering GFR, we calculated the efferent oncotic pressure (pie). Failure of GFR to change over a 24-hour period despite increases in ERPF suggested that both patient groups were at filtration pressure disequilibrium (FPD). This condition permits calculation of a unique glomerular ultrafiltration coefficient (Kf). Over a range of pressures for transcapillary hydraulic pressure (deltaP), such that 3 less than or equal to (deltaP - pie) less than or equal to 10 mm Hg (to simulate FPD), Kf was less than 0.08 ml . sec-1 . mm Hg-1 . 1.73 m-2 in azotemic, but exceeded this value in nonazotemic patients. Although a selective reduction of Kf is predicted to lower the fractional clearance of dextrans, these were significant elevated in azotemic relative to nonazotemic patients (molecular radii 30 - 40 A). A theoretical analysis of the latter data suggests that over the foregoing range of FPD, a 15 to 30% decline in deltaP combined with a 30 to 0% reduction in Kf from values in nonazotemic patients best explains the experimental findings in azotemic patients.

    View details for Web of Science ID A1981MK65500008

    View details for PubMedID 6170777

  • A REVIEW OF TRANS-CAPILLARY FLUID AND SOLUTE EXCHANGE IN THE RENAL GLOMERULUS MICROVASCULAR RESEARCH Robertson, C. R. 1980; 19 (2): 131-141

    View details for Web of Science ID A1980JK82400001

    View details for PubMedID 6155592

  • DETERMINATION OF ERYTHROCYTE VELOCITIES IN THE MAMMALIAN INNER RENAL MEDULLA BY A VIDEO VELOCITY-TRACKING SYSTEM MICROVASCULAR RESEARCH GUSSIS, G. L., Jamison, R. L., Robertson, C. R. 1979; 18 (3): 370-383

    View details for Web of Science ID A1979HW78700007

    View details for PubMedID 537513

  • RECENT FORMULATIONS OF THE URINARY CONCENTRATING MECHANISM - STATUS-REPORT KIDNEY INTERNATIONAL Jamison, R. L., Robertson, C. R. 1979; 16 (5): 537-545

    Abstract

    The status of the purely passive mode of solute concentration as of 1979 appears to be similar to that of the original countercurrent hypothesis 10 years ago. The passive mode concept has advanced our understanding of the concentrating process by qualitatively incorporating the permeability characteristics of tubule segments and the lack of an active transport process in the thin loop of Henle into a mechanism which has attractive economy and explanatory value. But in the final analysis some assumptions are not borne out by experimental findings (for example, the high urea concentration of fluid in the rat and hamster end-descending limb; the likelihood of net transepithelial addition of sodium chloride to the Psammomys descending limb; the removal of sodium chloride from the hamster ascending limb against an apparent electrochemical gradient under certain circumstances; and the osmotic lag between vasa recta blood and interstitium in the rat). Furthermore, when the known permeability and transport characteristics of the renal tubule are incorporated into a mathematic model of the passive operating mode, numerical simulations fail to establish a progressively hyperosmotic inner medulla. This does not rule out the applicability of the more general model (Eq. 1), particularly if evidence for some form of active transport in the inner medulla, heretofore lacking, is forthcoming.

    View details for Web of Science ID A1979HV72700001

    View details for PubMedID 398419

  • INFLUENCE OF MOLECULAR-CONFIGURATION ON THE PASSAGE OF MACROMOLECULES ACROSS THE GLOMERULAR CAPILLARY WALL JOURNAL OF GENERAL PHYSIOLOGY Bohrer, M. P., Deen, W. M., Robertson, C. R., Troy, J. L., BRENNER, B. M. 1979; 74 (5): 583-593

    Abstract

    The influence of molecular configuration on the filtration of macromolecules across glomerular capillary walls was examined by comparing fractional clearances of two uncharged polysaccharides of distinctly different molecular configuration in the Munich-Wistar rat. The macromolecules employed were dextran, a slightly branched polymer of glucopyranose, and ficoll, a highly cross-linked copolymer of sucrose and epichlorohydrin. Differences in effective shape between these two polymers were determined from measurements of several physical properties of aqueous solutions containing either dextran or ficoll. It was found that dextran is best represented as a prolate ellipsoid with axial ratios of 4, 9, and 16 for molecules with Stokes-Einstein radii of 22, 32, and 40 A, respectively. On the other hand, ficoll is more closely approximated as spherical since the axial ratio was found to be between 1 and 2 for all molecular sizes. Fractional clearances of dextran and ficoll ranging in effective radius from 18 to 44 A were determined in each of seven Munich-Wistar rats. Fractional clearances of dextran were found to be greater than those of ficoll, the difference being significant for molecular radii ranging from 24 to 44 A. In addition, as shown previously for dextran, ficoll was found to be neither secreted nor reabsorbed by the renal tubules. These results, therefore, suggest that in addition to molecular size and charge, molecular configuration is also a determinant of the filtration of macromolecules across the glomerular capillary wall.

    View details for Web of Science ID A1979HT96200003

    View details for PubMedID 512632

  • ERYTHROCYTE VELOCITY IN VASA RECTA - EFFECT OF ANTI-DIURETIC HORMONE AND SALINE LOADING AMERICAN JOURNAL OF PHYSIOLOGY GUSSIS, G. L., Robertson, C. R., Jamison, R. L. 1979; 237 (4): F326-F332

    View details for Web of Science ID A1979HR42500039

    View details for PubMedID 495726

  • PERMSELECTIVITY OF GLOMERULAR CAPILLARY WALL - FACILITATED FILTRATION OF CIRCULATING POLYCATIONS JOURNAL OF CLINICAL INVESTIGATION Bohrer, M. P., Baylis, C., Humes, H. D., Glassock, R. J., Robertson, C. R., BRENNER, B. M. 1978; 61 (1): 72-78

    Abstract

    To examine the electrostatic effects of fixed negative charges on the glomerular capillary wall, polydisperse [(3)H]DEAE dextran, a polycationic form of dextran, was infused into 10 Munich-Wistar rats. Fractional clearances of DEAE ranging in radius from 18 to 44A were determined in these rats, together with direct measurements of the forces and flows governing the glomerular filtration rate of water. These results were compared with data previously obtained in Munich-Wistar rats receiving tritiated neutral dextran (D) and polyanionic dextran sulfate (DS). Measured values for the determinants of the glomerular filtration rate of water in rats given DEAE were found to be essentially identical to those in rats given either D or DS. In addition, DEAE was shown to be neither secreted nor reabsorbed. Fractional clearances of polycationic DEAE were increased relative to both D and DS, the increase relative to D being significant for effective molecular radii ranging from 24 to 44A. Fractional DEAE clearances were also measured in a separate group of six Munich-Wistar rats in the early autologous phase of nephrotoxic serum nephritis (NSN). Fractional DEAE clearances in NSN rats were reduced significantly, relative to values measured in normal rats, for effective DEAE radii ranging from 18 to 42A. Moreover, in NSN rats, fixed negative charges on the glomerular capillary wall were greatly reduced, relative to non-NSN rats, as evidenced by a reduction in intensity of colloidal iron staining. Thus, in NSN rats, DEAE clearances were essentially indistinguishable from values obtained with both neutral D and polyanionic DS.

    View details for Web of Science ID A1978EG67200009

    View details for PubMedID 618914

  • MECHANISM OF ANGIOTENSIN II-INDUCED PROTEINURIA IN RAT AMERICAN JOURNAL OF PHYSIOLOGY Bohrer, M. P., Deen, W. M., Robertson, C. R., BRENNER, B. M. 1977; 233 (1): F13-F21

    Abstract

    To investigate the mechanism(s) of angiotensin II-induced proteinuria, polydisperse [3H]dextran (D) (radius = 18-42 A) was infused into seven Munich-Wistar rats before and during intravenous infusion of angiotensin II (AII), 0.35 microgram/kg per min. During AII infusion, UprotV rose approximately twofold, and the fractional clearances of D [(U/P)D/(U/P)In] increased significantly for dextrans with radii greater than 22 A. Single nephron filtration fraction increased, due to a measured rise in the glomerular transcapillary hydraulic pressure difference from 34 to 43 mmHg. Near constancy of single nephron glomerular filtration rate resulted, however, from the offsetting effect of a decrease in glomerular plasma flow rate from 83 to 60 nl/min. These measured hemodynamic changes were found, by the use of pore theory, to account to a large extent for the measured increases in (U/P)D/(U/P)In. In seven other rats, fractional clearances of polyanionic dex-ran sulfate (a more reliable marker of albumin filtration than D) were also found to increase significantly with AII, suggesting that the proteinuria induced by AII can be explained, in large part, by hemodynamic factors.

    View details for Web of Science ID A1977DR57900056

    View details for PubMedID 879319

  • DETERMINANTS OF TRANSGLOMERULAR PASSAGE OF MACROMOLECULES FEDERATION PROCEEDINGS Deen, W. M., Bohrer, M. P., Robertson, C. R., BRENNER, B. M. 1977; 36 (12): 2614-2618

    Abstract

    In addition to molecular size, at least two other factors influence the transglomerular passage of macromolecules. The hemodynamic determinants of glomerular filtration rate affect macromolecule transport by altering the volume flux through the glomerular capillary wall and the profile of macromolecule concentrations along a glomerular capillary. The electrostatic properties of the glomerular capillary wall markedly restrict the passage of circulating polyanions, relative to neutral macromolecules of similar size. In the normal animal, the combined effects of these various mechanisms ensure that only very small quantities of plasma proteins are filtered. In experimental proteinuric conditions such as nephrotoxic serum nephritis and puromycin-induced nephrosis, reduction in the fixed negative charges on the glomerular capillary wall appears to be largely responsible for the increased transglomerular passage of anionic macromolecules such as albumin. Other evidence suggests that hemodynamic factors may contribute to proteinuria under certain circumstance. The possibility of an increase in number and/or radius of glomerular "pores" being responsible for proteinuria, perhaps the most intuitively obvious and widely held view, has yet to receive direct experimental support.

    View details for Web of Science ID A1977EA22500014

    View details for PubMedID 913620

  • MECHANISMS OF PUROMYCIN-INDUCED DEFECTS IN TRANSGLOMERULAR PASSAGE OF WATER AND MACROMOLECULES JOURNAL OF CLINICAL INVESTIGATION Bohrer, M. P., Baylis, C., Robertson, C. R., BRENNER, B. M. 1977; 60 (1): 152-161
  • SOURCE OF INULIN IN SAMPLES OF VASA RECTA BLOOD ANNALS OF BIOMEDICAL ENGINEERING Johnston, P. A., LACY, F. B., SANJANA, V. M., Robertson, C. R., Jamison, R. L. 1977; 5 (1): 85-94

    View details for Web of Science ID A1977DB12500007

    View details for PubMedID 851266

  • TOTAL INTERNAL-REFLECTION TECHNIQUE FOR EXAMINATION OF PROTEIN ADSORPTION JOURNAL OF BIOMEDICAL MATERIALS RESEARCH Watkins, R. W., Robertson, C. R. 1977; 11 (6): 915-938

    Abstract

    A total internal-reflection fluorescence (TIRF) technique for examining protein adsorption at solid-liquid interfaces is described. For the representative case of adsorption of bovine gamma-globulin onto silicone rubber, the applicability of the technique to serveral important aspects of protein adsorption phenomena is demonstrated. Specifically, in addition to the tightly adsorbed protein layer observed herein and previously by maany others, the presence of a loosely adsorbed protein layer was also noted under conditions of either static or flowing protein solutions. Taking advantage of the continuous real-time measurements possible with TIRF, a rate constant for the protein adsorption step during laminar flow was estimated at both 25 and 37 degrees C. These results serve to demonstrate that the TIRF technique represents a significant and versatile new tool for the study of protein adsorption phenomena.

    View details for Web of Science ID A1977EE27700010

    View details for PubMedID 73542

  • EXAMINATION OF TRANSCAPILLARY WATER FLUX IN RENAL INNER MEDULLA AMERICAN JOURNAL OF PHYSIOLOGY SANJANA, V. M., Johnston, P. A., Robertson, C. R., Jamison, R. L. 1976; 231 (2): 313-318

    Abstract

    We recently demonstrated that net fluid uptake occurs in the capillary system of the inner medulla. To define the site of fluid uptake, the concentration of protein was determined in plasma from descending vasa recta at the base and tip of the exposed papilla in Munich-Wister rats. The vasa recta plasma-to-arterial plasma protein concentration ratio (VR/P) was 1.43 +/- 0.09 at the base and 1.66 +/- 0.09 at the tip. These results, which indicate fluid loss from the descending vasa recta, are difficult to explain on the basic of hydraulic and oncotic forces alone. The osmolality of the contents of descending vasa recta increased between base and tip (delta = 72 +/- 30 mosmol/kg H2O). If the increase in osmolality of plasma in descending vasa recta lags behind that of the adjacent medullary interstitium, a transcapillary osmotic driving force exists favoring water loss from descending vessels. It is concluded that fluid uptake by the inner medullary circulation occurs beyond descending vasa recta in interconnecting capillaries or ascending vasa recta. In our view the most likely interpretation of these results is that fluid movement across vasa recta in the inner medulla is influenced by three forces: those owing to transcapillary differences in osmotic, oncotic, and hydraulic pressures.

    View details for Web of Science ID A1976CC62600005

    View details for PubMedID 961881

  • PLATELET-AGGREGATION BY LAMINAR SHEAR AND BROWNIAN-MOTION ANNALS OF BIOMEDICAL ENGINEERING Chang, H. N., Robertson, C. R. 1976; 4 (2): 151-183

    View details for Web of Science ID A1976BY33300005

    View details for PubMedID 937782

  • PERMSELECTIVITY OF GLOMERULAR CAPILLARY WALL - STUDIES OF EXPERIMENTAL GLOMERULONEPHRITIS IN RAT USING NEUTRAL DEXTRAN JOURNAL OF CLINICAL INVESTIGATION CHANG, R. L., Deen, W. M., Robertson, C. R., Bennett, C. M., Glassock, R. J., BRENNER, B. M. 1976; 57 (5): 1272-1286
  • PERMSELECTIVITY OF GLOMERULAR CAPILLARY WALL - STUDIES OF EXPERIMENTAL GLOMERULONEPHRITIS IN RAT USING DEXTRAN SULFATE JOURNAL OF CLINICAL INVESTIGATION Bennett, C. M., Glassock, R. J., CHANG, R. L., Deen, W. M., Robertson, C. R., BRENNER, B. M. 1976; 57 (5): 1287-1294
  • DETERMINANTS OF GLOMERULAR-FILTRATION RATE ANNUAL REVIEW OF PHYSIOLOGY BRENNER, B. M., Deen, W. M., Robertson, C. R. 1976; 38: 9-19
  • WATER EXTRACTION FROM INNER MEDULLARY COLLECTING TUBULE SYSTEM - ROLE FOR UREA KIDNEY INTERNATIONAL SANJANA, V. M., Robertson, C. R., Jamison, R. L. 1976; 10 (2): 139-146

    Abstract

    Recent examinations of the inner medullary collecting tubule membrane in vitro have demonstrated that its reflection coefficient to urea (sigma urea) is significantly less than unity and less than sigma NaClhe presence of antidiuretic hormone. Fluid entering the inner medullary collecting tubule has a higher urea concentration and lower NaCl concentration than does the medullary interstitium, although total osmolarity is nearly equal on either side of the membrane. The transtubular difference in solute composition, together with the difference between sigma urea and sigma NaCl, should result in a driving force for extraction of water from the tubule. This hypothesis was examined in a differential analysis of water and solute fluxes across the collecting tubule epitheliu. The results indicate that this driving force contributes significantly to water extraction from the inner medullary collecting tubule.

    View details for Web of Science ID A1976CD47300002

    View details for PubMedID 966451

  • MOLECULAR SEPARATION BARRIERS AND THEIR APPLICATION TO CATALYTIC REACTOR DESIGN SEPARATION AND PURIFICATION METHODS Robertson, C. R., Michaels, A. S., WATERLAND, L. R. 1976; 5 (2): 301-332
  • PERMSELECTIVITY OF GLOMERULAR CAPILLARY WALL TO MACROMOLECULES .2. EXPERIMENTAL STUDIES IN RATS USING NEUTRAL DEXTRAN BIOPHYSICAL JOURNAL CHANG, R. L., Ueki, I. F., Troy, J. L., Deen, W. M., Robertson, C. R., BRENNER, B. M. 1975; 15 (9): 887-906

    Abstract

    To determine the permselectivity characteristics of the glomerular capillary wall, known molecular size fractions of [3H]dextran, prepared by gel chromatography, were infused into normally hydrated Wistar rats, thus permitting simultaneous measurement of Bowman's space/plasma water (BS/P) and urine/plasma water (U/P) concentration ratios, along with glomerular pressures and flows. Since (BS/P)inulin = 1.01 +/- 0.01 SE(n = 34, radius = approximately 14 A) and since (BS/P)dextran/(BS/P)inulin equaled (U/P)dextran/(U/P)inulin for dextrans ranging in molecular radius from 21 to 35 A, these findings validate that dextrans are neither secreted nor reabsorbed. For dextran radii of 20, 24, 28, 32, 36, 40, and 44 A, (U/P)dextran/(U/P)inulin averaged 0.99, 0.92, 0.69, 0.42, 0.19, 0.06, and 0.01, respectively. In accord with theoretical predictions that these fractional dextran clearances should vary appreciably with changes in glomerular transcapillary pressures and flows, an increase in glomerular plasma flow rate, induced in these same rats by plasma volume expansion, resulted in a highly significant lowering of fractional clearance of all but the smallest and largest dextrans studied. These findings emphasize that fractional solute clearances alone are inadequate to describe the permselective properties of the glomerular capillary wall unless glomerular pressures and flows are also known. This sensitivity of fractional dextran clearance to changes in plasma flow indicates that dextrans are transported across the capillary not only by bulk flow but also to an important extent by diffusion.

    View details for Web of Science ID A1975AQ82700003

    View details for PubMedID 1182263

  • HYDRAULIC AND ONCOTIC PRESSURE MEASUREMENTS IN INNER MEDULLA OF MAMMALIAN KIDNEY AMERICAN JOURNAL OF PHYSIOLOGY SANJANA, V. M., Johnston, P. A., Deen, W. M., Robertson, C. R., BRENNER, B. M., Jamison, R. L. 1975; 228 (6): 1921-1926

    Abstract

    The vasa recta are thought to play an important role in the transfer of water andsolutes within the renal medulla. Hydraulic pressures were measured in vasa recta onthe surface of the exposed papilla in young Munich Wistar rats, and blood was collected from these microvessels for determination of total protein concentration and calculation of colloid oncotic pressure. In descending vasa recta at the base of the exposed papilla, mean hydraulic pressure was 9.2 plus or minus 0.4 (SE) mmHg and plasma protein concentration averaged 7.1 plus or minus 0.4 g/100 ml. Corresponding valuesin ascending vasa recta at the same level were 7.8 plus or minus 0.4 mmHg and 5.6 plusor minus 0.3 g/100 ml. respectively. The protein concentrations correspond to calculated oncotic pressures of 26 and 18 mmHg in descending and ascending vasa recta, respectively. We interpret these findings as evidence for net water uptake by the vasa recta in the renal inner medulla for which the driving forces are the transcapillary hydraulic and oncotic pressure differences.

    View details for Web of Science ID A1975AJ22300047

    View details for PubMedID 1155623

  • PERMSELECTIVITY OF GLOMERULAR CAPILLARY WALL TO MACROMOLECULES .1. THEORETICAL CONSIDERATIONS BIOPHYSICAL JOURNAL CHANG, R. L., Robertson, C. R., Deen, W. M., BRENNER, B. M. 1975; 15 (9): 861-886

    Abstract

    The transport of macromolecules across the renal glomerular capillary wall has been described theoretically using flux equations based on (a) restricted transport through small pores, and (b) the Kedem-Katchalsky formulation. The various assumptions and limitations inherent in these two approaches are discussed. To examine the coupling between macromolecular solute transport and the determinants of glomerular filtration rate, these flux equations were combined with mass balance relations which allow for variations in the transmembrane driving forces along a glomerular capillary. It was predicted, using both pore theory and the Kedem-Katchalsky equations, that fractional solute clearance should be strongly dependent on the determinants of glomerular filtration rate when convection and diffusion both contribute to solute transport. When convection becomes the sole mechanism for transcapillary solute transport, however, fractional solute clearance is essentially independent of changes in the determinants of glomerular filtration rate. Consequently, unless diffusion is absent, fractional solute clearances alone are insufficient to characterize the permselective properties of the glomerular capillary wall, since these values may be altered by changes in glomerular pressures and flows as well as changes in the properties of the capillary wall per se.

    View details for Web of Science ID A1975AQ82700002

    View details for PubMedID 1237326

  • DYNAMICS OF GLOMERULAR ULTRAFILTRATION IN RAT .8. EFFECTS OF HEMATOCRIT CIRCULATION RESEARCH Myers, B. D., Deen, W. M., Robertson, C. R., BRENNER, B. M. 1975; 36 (3): 425-435

    Abstract

    This study was undertaken in an effort to examine the effects of selective variations in systemic hematocrit on the preglomerular, glomerular, and postglomerular micocirculation in the rat. By isovolemic exchange transfusions, systemic hematocrit (control 51 ml/100 ml) was either reduced (21 ml/100 ml, N equal 7 rats) or elevated (62 ml/100 ml, N equal 7). Single nephron glomerular filtration rate varied inversely and filtration fraction varied directly with the changes in hematocrit. The fall in filtration fraction with decreased hematocrit was due to a decline in the measured glomerular transcapillary hydraulic pressure difference and to a marked increased in the initial glomerular plasma flow rate. Afferent (RA)and efferent (RE) arteriolar resistance declined with the fall in hematocrit; RA fell proportionately more than did RE. The rise in filtration fraction with the elevation in hematocrit was due to a marked increase in in part due to a relatively greater rise in RE than in RA. These findings provide an attractive explanation for the general tendency for filtration fraction to vary directly with hematocrit in anemic and polycythemic states in man.

    View details for Web of Science ID A1975V842900007

    View details for PubMedID 1111999

  • EFFECT OF IONIC POLARIZABILITY ON ELECTRODIFFUSION IN LIPID BILAYER MEMBRANES JOURNAL OF MEMBRANE BIOLOGY Bradshaw, R. W., Robertson, C. R. 1975; 25 (1-2): 93-114

    Abstract

    Ion-carrier complexes and organic ions of similar size and shape have mobilities in lipid bilayer membranes which span several orders of magnitude. In this communication, an examination is made of the hypothesis that the basis for this unusually wide range of ionic mobilities is the potential energy barrier arising from image forces which selectively act on ions according to their polarizability. Using Poisson's equation to evaluate the electrostatic interaction between an ion and its surroundings, the potential energy barrier to ion transport due to image effects is computed, with the result that the potential energy barrier height depends strongly on ionic polarizability. Theoretical membrane potential energy profile calculations are used in conjunction with Nernst-Planck electrodiffusion equation to analyze the available mobility data for several ion-carrier complexes and lipid-soluble ions in lipid bilayer membranes. The variation among the mobilities of different ions is shown to be in agreement with theoretical predictions based on ionic polarizability and size. Furthermore, the important influence exerted by image forces on ion transport in lipid bilayer membranes compared to the frictional effect of membrane viscosity is established by contrasting available data on the activation energy of ionic conductivity with that for membrane fluidity.

    View details for Web of Science ID A1975BD96600006

    View details for PubMedID 1214289

  • GLOMERULAR ULTRAFILTRATION FEDERATION PROCEEDINGS Deen, W. M., ROBERTSO, C. R., BRENNER, B. M. 1974; 33 (1): 14-20

    View details for Web of Science ID A1974S030700004

    View details for PubMedID 4203956

  • PLATELET RETENTION IN COLUMNS PACKED WITH GLASS BEADS ANNALS OF BIOMEDICAL ENGINEERING Robertson, C. R., Chang, H. N. 1974; 2 (4): 361-391

    View details for Web of Science ID A1974V818400004

    View details for PubMedID 4458566

  • CONCENTRATION POLARIZATION IN AN ULTRAFILTERING CAPILLARY BIOPHYSICAL JOURNAL Deen, W. M., ROBERTSO, C. R., BRENNER, B. M. 1974; 14 (5): 412-431

    Abstract

    Concentration polarization, the accumulation of retained solute next to an ultrafiltering membrane, elevates osmotic pressure above that which would exist in the absence of polarization. For ultrafiltration in a cylindrical tube, use of the radially averaged solute concentration results in an underestimate of osmotic pressure, yielding an effective hydraulic permeability (k) less than the actual membrane hydraulic permeability (k(m)). The extent to which k and k(m) might differ in an ultrafiltering capillary has been examined theoretically by solution of the momentum and species transport equations for idealized capillaries with and without erythrocytes. For diameters, flow velocities, protein concentrations and diffusivities, and ultrafiltration pressures representative of the rat glomerular capillary network, results indicate that the effects of polarization are substantial without erythrocytes (k/k(m) = 0.7) and persist, but to a lesser extent, with erythrocytes (k/k(m) = 0.9), the reduction in polarization in the latter case being due to enhanced plasma mixing. In accord with recent experimental findings in rats, k is found to be relatively insensitive to changes in glomerular plasma flow rate.

    View details for Web of Science ID A1974S956500005

    View details for PubMedID 4836036

  • DYNAMICS OF GLOMERULAR ULTRAFILTRATION IN RAT .8. RESPONSE TO REDUCED RENAL MASS AMERICAN JOURNAL OF PHYSIOLOGY Deen, W. M., Maddox, D. A., ROBERTSO, C. R., BRENNER, B. M. 1974; 227 (3): 556-562

    View details for Web of Science ID A1974U350300008

    View details for PubMedID 4412873

  • THEORETICAL MODEL FOR ENZYMATIC CATALYSIS USING ASYMMETRIC HOLLOW FIBER MEMBRANES AICHE JOURNAL WATERLAN, L. R., Michaels, A. S., ROBERTSO, C. R. 1974; 20 (1): 50-60
  • TRANSCAPILLARY FLUID EXCHANGE IN RENAL CORTEX CIRCULATION RESEARCH Deen, W. M., ROBERTSO, C. R., BRENNER, B. M. 1973; 33 (1): 1-8
  • DYNAMICS OF GLOMERULAR ULTRAFILTRATION IN RAT .4. DETERMINATION OF ULTRAFILTRATION COEFFICIENT JOURNAL OF CLINICAL INVESTIGATION Deen, W. M., Troy, J. L., ROBERTSO, C. R., BRENNER, B. M. 1973; 52 (6): 1500-1508

    Abstract

    Pressures and flow rates were measured in accessible surface glomeruli of mutant Wistar rats under conditions deliberately designed to prevent achievement of filtration pressure equilibrium, that is, the equalization of transcapillary hydrostatic and oncotic pressures by the efferent end of the glomerulus as typically observed in the normal hydropenic rat. Disequilibrium was obtained at elevated levels of glomerular plasma flow (GPF) brought about by acute expansion of plasma volume with a volume of rat plasma equal to 5% of body weight. Glomerular hydrostatic and oncotic pressures measured at high GPF were used to calculate the ultrafiltration coefficient, K(f), the product of effective hydraulic permeability and surface area. GPF was then either lowered (by aortic constriction) or raised (by carotid occlusion) in order to examine the dependence of K(f) on GPF. The value of K(f) per glomerulus, 0.08 nl/(s.mm Hg), was found not to vary over an approximately twofold range of GPF. This finding, taken together with data from previous studies from this laboratory, leads us to conclude that plasma-flow dependence of glomerular filtration rate (GFR) results primarily from flow-induced changes in mean ultrafiltration pressure, rather than large changes in K(f).

    View details for Web of Science ID A1973P817200024

    View details for PubMedID 4703234

  • MODEL OF PERITUBULAR CAPILLARY CONTROL OF ISOTONIC FLUID REABSORPTION BY RENAL PROXIMAL TUBULE BIOPHYSICAL JOURNAL Deen, W. M., ROBERTSO, C. R., BRENNER, B. M. 1973; 13 (4): 340-358

Conference Proceedings


  • In-situ studies of flow-induced phenomena in Langmuir monolayers Maruyama, T., Friedenberg, M., Fuller, G. G., Frank, C. W., Robertson, C. R., Ferencz, A., Wegner, G. ELSEVIER SCIENCE SA. 1996: 76-83
  • NUTRIENT TRANSPORT AND CELLULAR MORPHOLOGY IN IMMOBILIZED CELL AGGREGATES FOWLER, J. D., Robertson, C. R. NEW YORK ACAD SCIENCES. 1990: 333-349

    View details for Web of Science ID A1990EX28200028

    View details for PubMedID 2192660

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