Bio

Academic Appointments


Professional Education


  • Ph.D., University of British Columbia, Physiology (2004)
  • B.Sc., University of British Columbia, Physiology (1997)

Publications

Journal Articles


  • Diminished Adenosine A1 Receptor Expression in Pancreatic a-Cells May Contribute to the Pathology of Type 1 Diabetes. Diabetes Yip, L., Taylor, C., Whiting, C. C., Fathman, C. G. 2013; 62 (12): 4208-4219

    Abstract

    Prediabetic NOD mice exhibit hyperglucagonemia, possibly due to an intrinsic α-cell defect. Here, we show that the expression of a potential glucagon inhibitor, the adenosine A1 receptor (Adora1), is gradually diminished in α-cells of NOD mice, autoantibody-positive (AA(+)) and overtly type 1 diabetic (T1D) patients during the progression of disease. We demonstrated that islet inflammation was associated with loss of Adora1 expression through the alternative splicing of Adora1. Expression of the spliced variant (Adora1-Var) was upregulated in the pancreas of 12-week-old NOD versus age-matched NOD.B10 (non-diabetes-susceptible) control mice and was detected in the pancreas of AA(+) patients but not in control subjects or overtly diabetic patients, suggesting that inflammation drives the splicing of Adora1. We subsequently demonstrated that Adora1-Var expression was upregulated in the islets of NOD.B10 mice after exposure to inflammatory cytokines and in the pancreas of NOD.SCID mice after adoptive transfer of activated autologous splenocytes. Adora1-Var encodes a dominant-negative N-terminal truncated isoform of Adora1. The splicing of Adora1 and loss of Adora1 expression on α-cells may explain the hyperglucagonemia observed in prediabetic NOD mice and may contribute to the pathogenesis of human T1D and NOD disease.

    View details for DOI 10.2337/db13-0614

    View details for PubMedID 24264405

  • Reduced DEAF1 function during type 1 diabetes inhibits translation in lymph node stromal cells by suppressing Eif4g3 JOURNAL OF MOLECULAR CELL BIOLOGY Yip, L., Creusot, R. J., Pager, C. T., Sarnow, P., Fathman, C. G. 2013; 5 (2): 99-110

    Abstract

    The transcriptional regulator deformed epidermal autoregulatory factor 1 (DEAF1) has been suggested to play a role in maintaining peripheral tolerance by controlling the transcription of peripheral tissue antigen genes in lymph node stromal cells (LNSCs). Here, we demonstrate that DEAF1 also regulates the translation of genes in LNSCs by controlling the transcription of the poorly characterized eukaryotic translation initiation factor 4 gamma 3 (Eif4g3) that encodes eIF4GII. Eif4g3 gene expression was reduced in the pancreatic lymph nodes of Deaf1-KO mice, non-obese diabetic mice, and type 1 diabetes patients, where functional Deaf1 is absent or diminished. Silencing of Deaf1 reduced Eif4g3 expression, but increased the expression of Caspase 3, a serine protease that degrades eIF4GII. Polysome profiling showed that reduced Eif4g3 expression in LNSCs resulted in the diminished translation of various genes, including Anpep, the gene for aminopeptidase N, an enzyme involved in fine-tuning antigen presentation on major histocompatibility complex (MHC) class II. Together these findings suggest that reduced DEAF1 function, and subsequent loss of Eif4g3 transcription may affect peripheral tissue antigen (PTA) expression in LNSCs and contribute to the pathology of T1D.

    View details for DOI 10.1093/jmcb/mjs052

    View details for Web of Science ID 000316701200004

    View details for PubMedID 22923498

  • Deaf1 isoforms control the expression of genes encoding peripheral tissue antigens in the pancreatic lymph nodes during type 1 diabetes NATURE IMMUNOLOGY Yip, L., Su, L., Sheng, D., Chang, P., Atkinson, M., Czesak, M., Albert, P. R., Collier, A., Turley, S. J., Fathman, C. G., Creusot, R. J. 2009; 10 (9): 1026-U107

    Abstract

    Type 1 diabetes may result from a breakdown in peripheral tolerance that is partially controlled by the expression of peripheral tissue antigens (PTAs) in lymph nodes. Here we show that the transcriptional regulator Deaf1 controls the expression of genes encoding PTAs in the pancreatic lymph nodes (PLNs). The expression of canonical Deaf1 was lower, whereas that of an alternatively spliced variant was higher, during the onset of destructive insulitis in the PLNs of nonobese diabetic (NOD) mice. We identified an equivalent variant Deaf1 isoform in the PLNs of patients with type 1 diabetes. Both the NOD mouse and human Deaf1 variant isoforms suppressed PTA expression by inhibiting the transcriptional activity of canonical Deaf1. Lower PTA expression resulting from the alternative splicing of DEAF1 may contribute to the pathogenesis of type 1 diabetes.

    View details for DOI 10.1038/ni.1773

    View details for Web of Science ID 000269120900017

    View details for PubMedID 19668219

  • Involvement of Adenosine Signaling in Controlling the Release of Ghrelin from the Mouse Stomach JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Yang, G. K., Yip, L., Fredholm, B. B., Kieffer, T. J., Kwok, Y. N. 2011; 336 (1): 77-86

    Abstract

    Ghrelin, a potent orexigenic hormone released from the stomach, is important in regulating energy metabolism. Abnormal ghrelin levels are associated with eating disorders and metabolic diseases. However, factors involved in the regulation of ghrelin release remain unclear. Here, we examined the involvement of adenosine signaling in the control of ghrelin release from the perfused mouse stomach. Adenosine stimulated ghrelin release concentration-dependently, and the A(2A) receptor-selective antagonists 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385) and 2-(2-furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine (SCH 58261) abolished the increased release. The A(2A) receptor-selective agonist 2-p-(2-carboxyethyl)phenethylamino-5-N-ethylcarboxamidoadenosine hydrochloride (CGS 21680) augmented ghrelin release concentration-dependently, whereas the A(1) receptor-selective agonist 2-chloro-N(6)-cyclopentyladenosine inhibited ghrelin release. In A(2A) receptor knockout mice, adenosine inhibited ghrelin release, and the A(1) receptor-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine blocked this inhibition. The adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride increased ghrelin release in wild-type and A(1) receptor knockout mice but not in A(2A) receptor knockout mice. Colocalization of ghrelin immunoreactivity with A(1) and A(2A) receptor immunoreactivities in the gastric nerve fibers were observed. Colocalization was also detected for ghrelin and A(1) receptor immunoreactivities in the gastric mucosa. Blockade of neural activities with tetrodotoxin abolished the stimulatory effect of adenosine on ghrelin release. In conclusion, adenosine exerts predominantly a tonic A(2A) receptor-mediated stimulatory action on gastric ghrelin release, whereas an A(1) receptor-mediated inhibitory action is also apparent when the tonic excitatory effect was removed.

    View details for DOI 10.1124/jpet.110.171280

    View details for Web of Science ID 000285338400011

    View details for PubMedID 20876230

  • Hypertonic stress regulates T cell function via pannexin-1 hemichannels and P2X receptors JOURNAL OF LEUKOCYTE BIOLOGY Woehrle, T., Yip, L., Manohar, M., Sumi, Y., Yao, Y., Chen, Y., Junger, W. G. 2010; 88 (6): 1181-1189

    Abstract

    Hypertonic saline (HS) resuscitation increases T cell function and inhibits posttraumatic T cell anergy, which can reduce immunosuppression and sepsis in trauma patients. We have previously shown that HS induces the release of cellular ATP and enhances T cell function. However, the mechanism by which HS induces ATP release and the subsequent regulation of T cell function by ATP remain poorly understood. In the present study, we show that inhibition of the gap junction hemichannel pannexin-1 (Panx1) blocks ATP release in response to HS, and HS exposure triggers significant changes in the expression of all P2X-type ATP receptors in Jurkat T cells. Blocking or silencing of Panx1 or of P2X1, P2X4, or P2X7 receptors blunts HS-induced p38 MAPK activation and the stimulatory effects of HS on TCR/CD28-induced IL-2 gene transcription. Moreover, treatment with HS or agonists of P2X receptors overcomes T cell suppression induced by the anti-inflammatory cytokine IL-10. These findings indicate that Panx1 hemichannels facilitate ATP release in response to hypertonic stress and that P2X1, P2X4, and P2X7 receptor activation enhances T cell function. We conclude that HS and P2 receptor agonists promote T cell function and thus, could be used to improve T cell function in trauma patients.

    View details for DOI 10.1189/jlb.0410211

    View details for Web of Science ID 000285867500016

    View details for PubMedID 20884646

  • Pannexin-1 hemichannel-mediated ATP release together with P2X1 and P2X4 receptors regulate T-cell activation at the immune synapse BLOOD Woehrle, T., Yip, L., Elkhal, A., Sumi, Y., Chen, Y., Yao, Y., Insel, P. A., Junger, W. G. 2010; 116 (18): 3475-3484

    Abstract

    Engagement of T cells with antigen-presenting cells requires T-cell receptor (TCR) stimulation at the immune synapse. We previously reported that TCR stimulation induces the release of cellular adenosine-5'-triphosphate (ATP) that regulates T-cell activation. Here we tested the roles of pannexin-1 hemichannels, which have been implicated in ATP release, and of various P2X receptors, which serve as ATP-gated Ca(2+) channels, in events that control T-cell activation. TCR stimulation results in the translocation of P2X1 and P2X4 receptors and pannexin-1 hemichannels to the immune synapse, while P2X7 receptors remain uniformly distributed on the cell surface. Removal of extracellular ATP or inhibition, mutation, or silencing of P2X1 and P2X4 receptors inhibits Ca(2+) entry, nuclear factors of activated T cells (NFAT) activation, and induction of interleukin-2 synthesis. Inhibition of pannexin-1 hemichannels suppresses TCR-induced ATP release, Ca(2+) entry, and T-cell activation. We conclude that pannexin-1 hemichannels and P2X1 and P2X4 receptors facilitate ATP release and autocrine feedback mechanisms that control Ca(2+) entry and T-cell activation at the immune synapse.

    View details for DOI 10.1182/blood-2010-04-277707

    View details for Web of Science ID 000283853200017

    View details for PubMedID 20660288

  • Autocrine regulation of T-cell activation by ATP release and P2X(7) receptors FASEB JOURNAL Yip, L., Woehrle, T., Corriden, R., Hirsh, M., Chen, Y., Inoue, Y., Ferrari, V., Insel, P. A., Junger, W. G. 2009; 23 (6): 1685-1693

    Abstract

    T-cell activation requires the influx of extracellular calcium, although mechanistic details regarding such activation are not fully defined. Here, we show that P2X(7) receptors play a key role in calcium influx and downstream signaling events associated with the activation of T cells. By real-time PCR and immunohistochemistry, we find that Jurkat T cells and human CD4(+) T cells express abundant P2X(7) receptors. We show, using a novel fluorescent microscopy technique, that T-cell receptor (TCR) stimulation triggers the rapid release of ATP (<100 microM). This release of ATP is required for TCR-mediated calcium influx, NFAT activation, and interleukin-2 (IL-2) production. TCR activation up-regulates P2X(7) receptor gene expression. Removal of extracellular ATP by apyrase or alkaline phosphatase treatment, inhibition of ATP release with the maxi-anion channel blocker gadolinium chloride, or siRNA silencing of P2X(7) receptors blocks calcium entry and inhibits T-cell activation. Moreover, lymphocyte activation is impaired in C57BL/6 mice that express poorly functional P2X(7) receptors, compared to control BALB/c mice, which express fully functional P2X(7) receptors. We conclude that ATP release and autocrine, positive feedback through P2X(7) receptors is required for the effective activation of T cells.

    View details for DOI 10.1096/fj.08-126458

    View details for Web of Science ID 000266652400008

    View details for PubMedID 19211924

  • A3 and P2Y2 receptors control the recruitment of neutrophils to the lungs in a mouse model of sepsis SHOCK Inoue, Y., Chen, Y., Hirsh, M. I., Yip, L., Junger, W. G. 2008; 30 (2): 173-177

    Abstract

    We have recently shown that A3 adenosine receptors and P2Y2 purinergic receptors play an important role in neutrophil chemotaxis. Chemotaxis of neutrophils to sites of infections is critical for immune defense. However, excessive accumulation of neutrophils in the lungs can cause acute lung tissue damage. Here we assessed the role of A3 and P2Y2 receptors in neutrophil sequestration to the lungs in a mouse model of sepsis. Sepsis was induced by cecal ligation and puncture (CLP) using adult male C57BL/6J mice (wild type [WT]), homozygous A3 receptor knockout (A3KO) mice, and P2Y2 receptor knockout (P2Y2KO) mice. Animals were killed 2, 4, 6, or 8 h after CLP, and peritoneal lavage fluid and blood were collected. Lungs were removed, and neutrophil infiltration was evaluated using elastase as a marker. Leukocyte and bacterial counts in peritoneal lavage fluid and blood samples were determined. Survival after sepsis was determined in a separate group. Leukocyte counts in the peritoneum were lower in A3KO and P2Y2KO mice than in WT mice. Conversely, initial leukocyte counts in the peripheral blood were higher in KO mice than in WT mice. Neutrophil sequestration to the lungs reached a maximum 2 h after CLP and remained significantly higher in WT mice compared with A3KO and P2Y2KO mice (P < 0.001). Survival after 24 h was significantly lower in WT mice (37.5%) than in A3KO or P2Y2KO mice (82.5%; P < 0.05). These data suggest that A3 and P2Y2 receptors are involved in the influx of neutrophils into the lungs after sepsis. Thus, pharmaceutical approaches that target these receptors might be useful to control acute lung tissue injury in sepsis.

    View details for DOI 10.1097/SHK.0b013e318160dad4

    View details for Web of Science ID 000257878500010

    View details for PubMedID 18091570

  • Hypertonic stress regulates T-cell function by the opposing actions of extracellular adenosine triphosphate and adenosine SHOCK Yip, L., Cheung, C. W., Corriden, R., Chen, Y., Insel, P. A., Junger, W. G. 2007; 27 (3): 242-250

    Abstract

    Hypertonic saline (HS) treatment promotes interleukin (IL)-2 production and enhances T-cell activation by the release of cellular adenosine triphosphate (ATP) that activates P2 nucleotide receptors. Released ATP can be hydrolyzed to adenosine, which inhibits T-cell activation. We examined if adenosine affects the response of T cells to HS treatment, and found that the amount of ATP released from T cells is a function of the HS concentration and duration of HS exposure. Physiologically relevant HS concentrations (<40 mmol/L) induced rapid ATP release, with the highest ATP concentrations released within 1 min. The released ATP was converted to adenosine, which opposed the enhancing effects of HS on IL-2 production. We found that Jurkat and CD4+ primary human T cells express most abundantly the A2A and A2B adenosine receptor subtypes, which mediate the suppressive effects of adenosine, as the A2 receptor agonist CGS 21680 suppressed IL-2 production, whereas the A2 receptor antagonist 3,7-dimethyl-1-(2-propynyl)xanthine augmented the enhancing effect of HS on T-cell function. Elimination of extracellular adenosine by adding exogenous adenosine deaminase also increased the enhancing effects of HS. These data suggest that the effect of HS treatment on T-cell function can be modulated with pharmacological agents that abolish the suppressive effects of adenosine formed from the ATP that is released in response to HS treatment.

    View details for DOI 10.1097/01.shk.0000245014.96419.3a

    View details for Web of Science ID 000244475300005

    View details for PubMedID 17304104

  • Hypertonic saline resuscitation: Efficacy may require early treatment in severely injured patients JOURNAL OF TRAUMA-INJURY INFECTION AND CRITICAL CARE Hashiguchi, N., Lum, L., Romeril, E., Chen, Y., Yip, L., Hoyt, D. B., Junger, W. G. 2007; 62 (2): 299-306

    Abstract

    Activation of polymorphonuclear neutrophils (PMN) is a critical event leading to host tissue injury and organ damage after trauma. Hypertonic saline (HS) resuscitation prevents PMN activation in vitro and in animal models. Here, we studied how clinical parameters and timing requirements influence the efficacy of HS in suppressing PMN activation.Twenty-six injured patients and 16 healthy volunteers were included as study subjects. To study how clinical parameters affect the efficacy of HS, whole blood samples from patients were collected 24 hours after admission, treated with HS and N-formyl-methionyl-leucyl-phenylalanine (fMLP), and PMN oxidative burst and degranulation were measured using flow cytometry. We studied the effect of timing on the ability of HS to inhibit PMN function by exposing blood of healthy volunteers to plasma samples from trauma patients before or after the addition of fMLP and HS.Age and gender did not significantly influence the effect of HS on PMN function. The suppressive effect of clinically relevant HS concentrations (20 mmol/L) on PMN oxidative burst correlated weakly with Sepsis Severity Score (SSS) and Acute Physiology and Chronic Health Evaluation II (APACHE II) score but not with the Injury Severity Score (ISS) or Multiple Organ Failure score (MOF). There was no correlation between any of these clinical scores and degranulation. HS was significantly less effective in suppressing oxidative burst of PMN from patients with ISS >10, APACHE II >5, MOF >0, or SSS >1 compared with patients with ISS < or =10, APACHE II < or =5, MOF = 0, or SSS < or =1. HS more effectively suppressed PMN activation when PMN were pretreatment with HS, whereas it was less effective on PMN previously primed in vivo or in vitro by adding trauma plasma. HS was ineffective on PMN previously stimulated in vitro with fMLP.Our data suggest that HS resuscitation may prevent PMN activation most effectively when patients are treated with HS early in the field.

    View details for DOI 10.1097/01.ta.0000222956.88760.33

    View details for Web of Science ID 000244333300007

    View details for PubMedID 17297316

  • ATP release guides neutrophil chemotaxis via P2Y2 and A3 receptors SCIENCE Chen, Y., Corriden, R., Inoue, Y., Yip, L., Hashiguchi, N., Zinkernagel, A., Nizet, V., Insel, P. A., Junger, W. G. 2006; 314 (5806): 1792-1795

    Abstract

    Cells must amplify external signals to orient and migrate in chemotactic gradient fields. We find that human neutrophils release adenosine triphosphate (ATP) from the leading edge of the cell surface to amplify chemotactic signals and direct cell orientation by feedback through P2Y2 nucleotide receptors. Neutrophils rapidly hydrolyze released ATP to adenosine that then acts via A3-type adenosine receptors, which are recruited to the leading edge, to promote cell migration. Thus, ATP release and autocrine feedback through P2Y2 and A3 receptors provide signal amplification, controlling gradient sensing and migration of neutrophils.

    View details for DOI 10.1126/science.1132559

    View details for Web of Science ID 000242833600064

    View details for PubMedID 17170310

  • Hypertonic saline enhances neutrophil elastase release through activation of P2 and A3 receptors AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY Chen, Y., Hashiguchi, N., Yip, L., Junger, W. G. 2006; 290 (4): C1051-C1059

    Abstract

    Hypertonic saline (HS) holds promise as a novel resuscitation fluid for the treatment of trauma patients because HS inhibits polymorphonuclear neutrophil (PMN) activation and thereby prevents host tissue damage and associated posttraumatic complications. However, depending on conditions of cell activation, HS can increase PMN degranulation, which could exacerbate tissue damage in trauma victims. The cellular mechanism by which HS increases degranulation is unknown. In the present study, we tested whether HS-induced ATP release from PMN and feedback via P1 and/or P2 receptors may be involved in the enhancement of degranulation by HS. We found that HS enhances elastase release and ERK and p38 MAPK activation when HS is added after activation of PMN with formyl peptide (fMLP) or phorbol ester (PMA). Agonists of P2 nucleotide and A3 adenosine receptors mimicked these enhancing effects of HS, whereas antagonists of A3 receptors or removal of extracellular ATP with apyrase diminished the response to HS. A1 adenosine receptor antagonists increased the enhancing effect of HS, whereas A1 receptor agonists inhibited elastase release. These data suggest that HS upregulates degranulation via ATP release and positive feedback through P2 and A3 receptors. We propose that these feedback mechanisms can serve as potential pharmacological targets to fine-tune the clinical effectiveness of HS resuscitation.

    View details for DOI 10.1152/ajpcell.00216.2005

    View details for Web of Science ID 000236573300013

    View details for PubMedID 16282197

  • Surface expression of HSP72 by LPS-stimulated neutrophils facilitates gamma delta T cell-mediated killing EUROPEAN JOURNAL OF IMMUNOLOGY Hirsh, M. I., Hashiguchi, N., Chen, Y., Yip, L., Junger, W. G. 2006; 36 (3): 712-721

    Abstract

    During inflammation and sepsis, accumulation of activated neutrophils causes lung tissue damage and organ failure. Effective clearance of neutrophils reduces the risk of organ failure; however, its mechanisms are poorly understood. Because lungs are rich in gammadeltaT cells, we investigated the physiological role of these cells in the protection of lung tissue from infiltrating neutrophils. In a mouse model of sepsis, we found that the lungs of survivors contained significantly higher numbers of gammadeltaT cells than those of mice that died from sepsis. The number of gammadeltaT cells correlated inversely with the number of neutrophils in the lungs and with the degree of lung tissue damage. LPS rapidly elicited the expression of heat shock protein (HSP) 72 on the surface of human neutrophils. Inhibitors of transcription, protein synthesis, and intracellular protein transport blocked HSP72 expression, indicating that de novo synthesis is required. gammadeltaT cells targeted and rapidly killed LPS-treated neutrophils through direct cell-to-cell contact. Pre-treatment with neutralizing antibodies to HSP72 diminished neutrophil killing. Our data indicate that HSP72 expression on the cell surface predisposes inflamed neutrophils to killing by gammadeltaT cells. This intercellular exchange may allow gammadeltaT cells to resolve inflammation and limit host tissue damage during sepsis.

    View details for DOI 10.1002/eji.200535422

    View details for Web of Science ID 000236457400021

    View details for PubMedID 16482515

  • Effect of omeprazole on gastric adenosine A(1) and A(2A) receptor gene expression and function JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Yip, L., Leung, H. C., Kwok, Y. N. 2004; 311 (1): 180-189

    Abstract

    Adenosine has been shown to inhibit immunoreactive gastrin (IRG) release and to stimulate somatostatin-like immunoreactivity (SLI) release by activating adenosine A(1) and A(2A) receptors, respectively. Since the synthesis and release of gastrin and somatostatin are regulated by the acid secretory state of the stomach, the effect of achlorhydria on A(1) and A(2A) receptor gene expression and function was examined. Omeprazole-induced achlorhydria was shown to suppress A(1) and A(2A) receptor gene expression in the antrum and corporeal mucosa, but not in the corporeal muscle. Omeprazole treatment produced reciprocal changes in A(1) receptor and gastrin gene expression, and parallel changes in A(2A) receptor and somatostatin gene expression. The localization of A(1) and A(2A) receptors on gastrinsecreting G-cells and somatostatin-secreting D-cells, respectively, suggests that changes in adenosine receptor expression may modulate the synthesis and release of gastrin and somatostatin. Thus, the effect of omeprazole on adenosine receptor-mediated changes in IRG and SLI release was also examined in the vascularly perfused rat stomach. After omeprazole treatment, the A(1) receptor-mediated inhibition of IRG and SLI release induced by N(6)-cyclopentyladenosine (A(1) receptor-selective agonist) was not altered, but the A(2A) receptor-mediated augmentation of SLI release induced by 2-p-(2-carboxyethyl-)phenethylamino-5'-N-ethylcarboxamidoadenosine (A(2A)-selective agonist) was significantly attenuated. These findings agree well with the corresponding omeprazole-induced decrease in antral A(2A) receptor mRNA expression. Overall, the present study suggests that adenosine receptor gene expression and function may be altered by omeprazole treatment. Acid-dependent changes in adenosine receptor expression may represent a novel purinergic regulatory feedback mechanism in controlling gastric acid secretion.

    View details for DOI 10.1124/jpet.104.069708

    View details for Web of Science ID 000223896100022

    View details for PubMedID 15155771

  • Role of adenosine A(1) receptor in the regulation of gastrin release JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Yip, L., Chi, H., Leung, H., Kwok, Y. N. 2004; 310 (2): 477-487

    Abstract

    Adenosine has been demonstrated to inhibit gastric acid secretion. In the rat stomach, this inhibitory effect may be mediated indirectly by the inhibition of gastrin release. Results show that the A(1) receptor agonist N(6)-cyclopentyladenosine (CPA) suppressed immunoreactive gastrin (IRG) release in a concentration-dependent manner. CPA significantly inhibited IRG release at 0.001 microM and maximally inhibited IRG release at 1 microM. At concentrations of 0.001 to 0.1 microM, the A(2A) receptor-selective agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine and A(3) receptor-selective agonist 1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-beta-d-ribofuranuronamide, had no effect on IRG release, suggesting the involvement of A(1) receptors. In agreement, the A(1) receptor-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine abolished adenosine-induced inhibition of IRG release. Results of immunohistochemistry experiments reveal the presence of A(1) receptor immunoreactivity on mucosal G-cells and D-cells, and the gastric plexi, but not parietal cells, suggesting that adenosine may act directly on G-cells or indirectly on the gastric plexi to modulate IRG release. The structure of the mucosal A(1) receptor was found to be identical to that in the rat brain. Alternative splicing within the coding region of this receptor did not occur. A real-time reverse transcription-polymerase chain reaction assay was developed to measure gastric A(1) receptor gene expression. The highest level of gastric A(1) receptor mRNA was found in the corporeal muscle. However, this level was significantly lower in comparison with the striatum. In conclusion, this study shows that adenosine may suppress IRG release, at least in part, by activating A(1) receptors localized on G-cells and may consequently result in an inhibition of gastric acid secretion.

    View details for DOI 10.1124/jpet.104.066654

    View details for Web of Science ID 000222728500007

    View details for PubMedID 15044554

  • Role of adenosine A(2A) receptor in the regulation of gastric somatostatin release JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Yip, L., Kwok, Y. N. 2004; 309 (2): 804-815

    Abstract

    Adenosine has been demonstrated to inhibit gastric acid secretion. In the rat stomach, this inhibitory effect may be mediated indirectly by increasing the release of somatostatin-like immunoreactivity (SLI). Results show that adenosine analogs augmented SLI release in the isolated vascularly perfused rat stomach. The rank order of potency of the analogs in stimulating SLI release was 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680) approximately 5'-N-ethylcarboxamidoadenosine > 2-chloroadenosine > R-(-)-N(6)-(2-phenylisopropyl)adenosine >1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-beta-d-ribofuranuronamide > N(6)-cyclopentyladenosine approximately N(6)-cyclohexyladenosine > S-(+)-N(6)-(2-phenylisopropyl) adenosine, suggesting the involvement of the A(2A) receptor. In agreement, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a] [1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385), an A(2A) receptor antagonist, was shown to abolish the adenosine- and CGS 21680-stimulated SLI release. Immunohistochemical studies reveal the presence of A(2A) receptor immunoreactivity on the gastric plexi and mucosal D-cells, but not on parietal cells and G-cells, suggesting that adenosine may act directly on D-cells or indirectly on the gastric plexi to augment SLI release. The present study also demonstrates that the structure of the mucosal A(2A) receptor is identical to that in the rat brain, and that alternative splicing of this gene does not occur. A real-time reverse transcription-polymerase chain reaction assay has also been established to quantify the levels of A(2A) receptor mRNA. Results show that gastric tissues contained significantly lower levels of A(2A) receptor mRNA compared with the striatum. The lowest level was detected in the mucosa. In conclusion, adenosine may act on A(2A) receptors to augment SLI release and consequently control gastric acid secretion.

    View details for DOI 10.1124/jpet.103.061986

    View details for Web of Science ID 000220972900046

    View details for PubMedID 14742743

  • Cellular localization and distribution of neurokinin-1 receptors in the rat stomach AUTONOMIC NEUROSCIENCE-BASIC & CLINICAL Yip, L., Kwok, Y. N., Buchan, A. M. 2003; 104 (2): 95-108

    Abstract

    In the stomach, the majority of substance P's effects are mediated by the activation of neurokinin-1 (NK1) receptors. The gastric cellular distribution of these receptors in Wistar and Sprague-Dawley rats was determined using immunocytochemistry. The localization of the NK1 receptors with respect to von Willebrand's factor, protein gene product 9.5, substance P, vasoactive intestinal peptide, and calcitonin gene-related peptide was also determined. Results show that NK1 receptor immunoreactivity was dependent on the duration of fixation. In corpus and antrum tissues that were fixed in 4% paraformaldehyde for 30 min, the presence of NK1 receptor immunoreactivity was demonstrated on nerve fibers throughout the stomach, on the surface and in the cytoplasm of myenteric cell bodies, on circular smooth muscle cells, and on vascular endothelial cells. This was observed in tissues from both rodent strains. Overnight fixation in the same fixative, however, demonstrated the presence of NK1 receptor immunoreactivity only on nerve fibers and cell bodies of the myenteric plexus, and on circular smooth muscle cells. In 30-min fixed tissues, the localization of NK1R immunoreactivity on vascular endothelial cells and nerve fibers was confirmed by co-localization with von Willebrand's factor and protein gene product 9.5 immunoreactivity, respectively. In both rodent strains, NK1 receptor immunoreactivity was co-localized with substance P immunoreactivity on nerve fibers of the longitudinal and circular muscle. In the Wistar rat, NK1 receptor immunoreactivity was co-localized with vasoactive intestinal peptide immunoreactivity or calcitonin gene-related peptide immunoreactivity throughout the stomach. However, in the Sprague-Dawley rat, NK1 receptor immunoreactivity was only co-localized with calcitonin gene-related peptide immunoreactivity in a minority of fibers of the circular muscle. The overall results of this study show that the antigenic epitopes of the NK1 receptor are sensitive to overfixation. When tissues were not overfixed, NK1 receptor immunoreactivity was distributed more extensively throughout the rat stomach than has been described previously. The results of this study provide the anatomical basis for many of the actions of substance P in the rat stomach.

    View details for DOI 10.1016/S1566-0702(02)00293-X

    View details for Web of Science ID 000181995600004

    View details for PubMedID 12648611

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