Duk-Su Koh

University of Washington Seattle, Seattle, Washington, United States

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Publications (25)121.1 Total impact

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    ABSTRACT: Melatonin secretion from the pineal gland is triggered by norepinephrine released from sympathetic terminals at night. In contrast, cholinergic and parasympathetic inputs, by activating nicotinic cholinergic receptors (nAChR), have been suggested to counterbalance the noradrenergic input. Here we investigated whether adrenergic signaling regulates nAChR channels in rat pinealocytes. Acetylcholine or the selective nicotinic receptor agonist, 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), activated large nAChR currents in whole-cell patch clamp experiments. Norepinephrine (NE) reduced the nAChR currents, an effect partially mimicked by a β-adrenergic receptor agonist, isoproterenol, and blocked by a β-adrenergic receptor antagonist, propranolol. Increasing intracellular cAMP levels using membrane-permeable 8-Br-cAMP or cBiMPS also reduced nAChR activity, mimicking the effects of NE and isoproterenol. Further, removal of ATP from the intracellular pipette solution blocked the reduction of nAChR currents, suggesting involvement of protein kinases. Indeed protein kinase A inhibitors, H-89 and Rp-cAMPS, blocked the modulation of nAChR by adrenergic stimulation. After the down-modulation by NE, nAChR channels mediated a smaller Ca(2+) influx and less membrane depolarization from the resting potential. Together these results suggest that NE released from sympathetic terminals at night attenuates nicotinic cholinergic signaling.
    AJP Cell Physiology 02/2014; · 3.71 Impact Factor
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    Jong Bae Seo, Mark Moody, Duk-Su Koh
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    ABSTRACT: Abstract Many epithelial cells form polarized monolayers under in vivo and in vitro conditions. Typically, epithelial cells are cultured for differentiation on insert systems where cells are plated on a porous filter membrane. Although the cultured monolayers have been a standard system to study epithelial physiology, there are some limits: The epithelial cells growing inside the commercial inserts are not optimal to visualize directly through lenses on inverted microscopes. The cell images are optically distorted and background fluorescence is bright due to the filter membrane positioned between the cells and the lens. In addition, the cells are not easily accessible by electrodes due to the presence of tall side walls. Here, we present the design, fabrication, and practical applications of an improved system for analysis of polarized epithelial monolayers. This new system allows (1) direct imaging of cells without an interfering filter membrane, (2) electrophysiological measurements, and (3) detection of apical secretion with minimal dilution. Therefore, our culture method is optimized to study differentiated epithelial cells at the single-cell and subcellular levels, and can be extended to other cell types with minor modifications.
    Physiological reports. 01/2014; 2(4):e12002.
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    ABSTRACT: Store-operated Ca(2+) channels (SOCs) are activated by depletion of intracellular Ca(2+) stores following agonist-mediated Ca(2+) release. Previously we demonstrated that Ca(2+) influx through SOCs elicits exocytosis efficiently in pancreatic duct epithelial cells (PDEC). Here we describe the biophysical, pharmacological, and molecular properties of the duct epithelial SOCs using Ca(2+) imaging, whole-cell patch-clamp, and molecular biology. In PDEC, agonists of purinergic, muscarinic, and adrenergic receptors coupled to phospholipase C activated SOC-mediated Ca(2+) influx as Ca(2+) was released from intracellular stores. Direct measurement of [Ca(2+)] in the ER showed that SOCs greatly slowed depletion of the ER. Using IP3 or thapsigargin in the patch pipette elicited inwardly rectifying SOC currents. The currents increased ∼8-fold after removal of extracellular divalent cations, suggesting competitive permeation between mono- and divalent cations. The current was completely blocked by high doses of La(3+) and 2-aminoethoxydiphenyl borate (2-APB) but only partially depressed by SKF-96365. In polarized PDEC, SOCs were localized specifically to the basolateral membrane. RT-PCR screening revealed the expression of both STIM and Orai proteins for the formation of SOCs in PDEC. By expression of fluorescent STIM1 and Orai1 proteins in PDEC, we confirmed that colocalization of the two proteins increases after store depletion. In conclusion, basolateral Ca(2+) entry through SOCs fills internal Ca(2+) stores depleted by external stimuli and will facilitate cellular processes dependent on cytoplasmic Ca(2+) such as salt and mucin secretion from the exocrine pancreatic ducts.
    Cell calcium 08/2013; · 4.29 Impact Factor
  • Duk-Su Koh, Mark Moody, Junghyo Jo
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    ABSTRACT: Here we present a convenient method for easy hand selection of enzymatically isolated small tissues such as islets of Langerhans. Islets are continuously collected in a micropipette tip connected to a peristaltic pump. After entering the conical micropipette tip, the islets are quickly dragged up by solution flow, but this movement subsequently decreases as the flow rate decreases. Thus, the islets are trapped at a specific height where downward gravitation balances upward buoyancy and the drag provided by solution flow. Our device allows more efficient isolation of islets compared to conventional manual collection methods.
    BioTechniques 07/2013; 55(1):34-7. · 2.40 Impact Factor
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    ABSTRACT: Alcohol abuse is a major cause of pancreatitis. However alcohol toxicity has not been fully elucidated in the pancreas and little is known about the effect of alcohol on pancreatic ducts. We report the molecular mechanisms of ethanol-induced damage of pancreatic duct epithelial cells (PDEC). Ethanol treatment for 1, 4, and 24 h resulted in cell death in a dose-dependent manner. The ethanol-induced cell damage was mainly apoptosis due to generation of reactive oxygen species (ROS), depolarization of mitochondrial membrane potential (MMP), and activation of caspase-3 enzyme. The antioxidant N-acetylcysteine (NAC) attenuated these cellular responses and reduced cell death significantly, suggesting a critical role for ROS. Acetaldehyde, a metabolic product of alcohol dehydrogenase, induced significant cell death, depolarization of MMP, and caspase-3 activation as ethanol and this damage was also averted by NAC. Reverse transcription-polymerase chain reaction revealed the expression of several subtypes of alcohol dehydrogenase and acetaldehyde dehydrogenase. Nuclear magnetic resonance spectroscopy data confirmed the accumulation of acetaldehyde in ethanol-treated cells, suggesting that acetaldehyde formation can contribute to alcohol toxicity in PDEC. Finally, ethanol increased the leakage of PDEC monolayer which was again attenuated by NAC. In conclusion, ethanol induces apoptosis of PDEC and thereby may contribute to the development of alcohol-induced pancreatitis.
    PLoS ONE 01/2013; 8(11):e81893. · 3.53 Impact Factor
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    ABSTRACT: In most eukaryotic cells, microtubules and filamentous actin (F-actin) provide tracks on which intracellular organelles move using molecular motors. Here we report that cytoplasmic movement of both mitochondria and lysosomes is slowed by F-actin meshwork formation in pancreatic duct epithelial cells (PDEC). Mitochondria and lysosomes were labeled with fluorescent Mitotracker Red CMXRos and Lysotracker Red DND-99, respectively, and their movements were monitored using epi-fluorescence and confocal microscopy. Mitochondria and lysosomes moving actively at rest stopped rapidly within several seconds after an intracellular Ca(2+) rise induced by activation of P2Y(2) purinergic receptors. The 'freezing' of the organelles was inhibited by blocking the Ca(2+) rise or by pretreatment with latrunculin B, an inhibitor of F-actin formation. Indeed, this freezing effect on the organelles was accompanied by the formation of F-actin in the whole cytoplasm as stained with Alexa 488-phalloidin in fixed PDEC. For real-time monitoring of F-actin formation in live cells, we expressed sGFP-fimbrin actin binding domain2 (fABD2) in PDEC. Rapid recruitment of the fluorescent probe near the nucleus and lysosomes suggested dense F-actin formation around intracellular structures. The development of F-actin paralleled that of organelle freezing. We conclude that rapid Ca(2+)-dependent F-actin formation physically restrains intracellular organelles and reduces their mobility non-selectively in PDEC.
    Cell calcium 05/2012; 51(6):459-69. · 4.29 Impact Factor
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    Duk-Su Koh, Jung-Hwa Cho, Liangyi Chen
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    ABSTRACT: Glucose supply fluctuates between meal and fasting periods and its consumption by the body varies greatly depending on bodily metabolism. Pancreatic islets of Langerhans secrete various endocrine hormones including insulin and glucagon to keep blood glucose level relatively constant. Additionally, islet hormones regulate activity of neighboring cells as local autocrine or paracrine modulators. Moreover, islet cells release neurotransmitters such as glutamate and γ-aminobutyric acid (GABA) to gain more precise regulation of hormones release kinetics. Excitatory glutamate is co-released with glucagon from α-cells and activates glutamate receptors in the neighboring cells. GABA released from β-cells was shown to inhibit α-cells but to activate β-cells by acting GABA(A) receptors. This review summarizes the recent progress in understanding the paracrine/autocrine interactions in islets.
    Journal of Molecular Neuroscience 04/2012; 48(2):429-40. · 2.89 Impact Factor
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    ABSTRACT: This article describes a perfusion system for biophysical single cell experiments at the physiological temperature. Our system regulates temperature of test solutions using a small heat exchanger that includes several capillaries. Water circulating inside the heat exchanger warms or cools test solutions flowing inside the capillaries. Temperature-controlled solutions are delivered directly to a single cell(s) through a multibarreled manifold that switches solutions bathing a cell in less than 1s. This solution exchange is optimal for patch clamp, single-cell microamperometry, and microfluorometry experiments. Using this system, we demonstrate that exocytosis from pancreatic β cells and activation of TRPV1 channels are temperature sensitive. We also discuss how to measure local temperature near a single cell under investigation.
    Journal of neuroscience methods 07/2011; 199(1):35-42. · 2.30 Impact Factor
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    ABSTRACT: Exocytosis is evoked by intracellular signals, including Ca(2+) and protein kinases. We determined how such signals interact to promote exocytosis in exocrine pancreatic duct epithelial cells (PDECs). Exocytosis, detected using carbon-fiber microamperometry, was stimulated by [Ca(2+)](i) increases induced either through Ca(2+) influx using ionomycin or by activation of P2Y2 or protease-activated receptor 2 receptors. In each case, the exocytosis was strongly potentiated when cyclic AMP (cAMP) was elevated either by activating adenylyl cyclase with forskolin or by activating the endogenous vasoactive intestinal peptide receptor. This potentiation was completely inhibited by H-89 and partially blocked by Rp-8-Br-cAMPS, inhibitors of protein kinase A. Optical monitoring of fluorescently labeled secretory granules showed slow migration toward the plasma membrane during Ca(2+) elevations. Neither this Ca(2+)-dependent granule movement nor the number of granules found near the plasma membrane were detectably changed by raising cAMP, suggesting that cAMP potentiates Ca(2+)-dependent exocytosis at a later stage. A kinetic model was made of the exocytosis stimulated by UTP, trypsin, and Ca(2+) ionophores with and without cAMP increase. In the model, without a cAMP rise, receptor activation stimulates exocytosis both by Ca(2+) elevation and by the action of another messenger(s). With cAMP elevation the docking/priming step for secretory granules was accelerated, augmenting the releasable granule pool size, and the Ca(2+) sensitivity of the final fusion step was increased, augmenting the rate of exocytosis. Presumably both cAMP actions require cAMP-dependent phosphorylation of target proteins. cAMP-dependent potentiation of Ca(2+)-induced exocytosis has physiological implications for mucin secretion and, possibly, for membrane protein insertion in the pancreatic duct. In addition, mechanisms underlying this potentiation of slow exocytosis may also exist in other cell systems.
    The Journal of General Physiology 05/2010; 135(5):527-43. · 4.73 Impact Factor
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    ABSTRACT: Pancreatic islet cells use neurotransmitters such as l-glutamate to regulate hormone secretion. We determined which cell types in mouse pancreatic islets express ionotropic glutamate receptor channels (iGluRs) and describe the detailed biophysical properties and physiological roles of these receptors. Currents through iGluRs and the resulting membrane depolarization were measured with patch-clamp methods. Ca(2+) influx through voltage-gated Ca(2+) channels and Ca(2+)-evoked exocytosis were detected by Ca(2+) imaging and carbon-fiber microamperometry. Whereas iGluR2 glutamate receptor immunoreactivity was detected using specific antibodies in immunocytochemically identified mouse alpha- and beta-cells, functional iGluRs were detected only in the alpha-cells. Fast application of l-glutamate to cells elicited rapidly activating and desensitizing inward currents at -60 mV. By functional criteria, the currents were identified as alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors. They were activated and desensitized by AMPA, and were activated only weakly by kainate. The desensitization by AMPA was inhibited by cyclothiazide, and the currents were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Islet iGluRs showed nonselective cation permeability with a low Ca(2+) permeability (P(Ca)/P(Na) = 0.16). Activation of the AMPA receptors induced a sequence of cellular actions in alpha-cells: 1) depolarization of the membrane by 27 +/- 3 mV, 2) rise in intracellular Ca(2+) mainly mediated by voltage-gated Ca(2+) channels activated during the membrane depolarization, and 3) increase of exocytosis by the Ca(2+) rise. In conclusion, iGluRs expressed in mouse alpha-cells resemble the low Ca(2+)-permeable AMPA receptor in brain and can stimulate exocytosis.
    Endocrinology 02/2010; 151(4):1541-50. · 4.72 Impact Factor
  • Gastroenterology 01/2010; 138(5). · 12.82 Impact Factor
  • Biophysical Journal 01/2009; 96(3). · 3.67 Impact Factor
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    ABSTRACT: Elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) triggers exocytosis of secretory granules in pancreatic duct epithelia. In this study, we find that the signal also controls granule movement. Motions of fluorescently labeled granules stopped abruptly after a [Ca(2+)](i) increase, kinetically coincident with formation of filamentous actin (F-actin) in the whole cytoplasm. At high resolution, the new F-actin meshwork was so dense that cellular structures of granule size appeared physically trapped in it. Depolymerization of F-actin with latrunculin B blocked both the F-actin formation and the arrest of granules. Interestingly, when monitored with total internal reflection fluorescence microscopy, the immobilized granules still moved slowly and concertedly toward the plasma membrane. This group translocation was abolished by blockers of myosin. Exocytosis measured by microamperometry suggested that formation of a dense F-actin meshwork inhibited exocytosis at small Ca(2+) rises <1 microm. Larger [Ca(2+)](i) rises increased exocytosis because of the co-ordinate translocation of granules and fusion to the membrane. We propose that the Ca(2+)-dependent freezing of granules filters out weak inputs but allows exocytosis under stronger inputs by controlling granule movements.
    Traffic 01/2009; 10(4):392-410. · 4.65 Impact Factor
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    ABSTRACT: Glutamate transporters are expressed throughout the CNS where their major role is to clear released glutamate from presynaptic terminals. Here, we report a novel function of the transporter in rat pinealocytes. This electrogenic transporter conducted inward current in response to L-glutamate and L- or D-aspartate and depolarized the membrane in patch-clamp experiments. Ca2+ imaging demonstrated that the transporter-mediated depolarization induced a significant Ca2+ influx through voltage-gated Ca2+ channels. The Ca2+ rise finally evoked glutamate exocytosis as detected by carbon-fiber amperometry and by HPLC. In pineal slices with densely packed pinealocytes, glutamate released from the cells effectively activated glutamate transporters in neighboring cells. The Ca2+ signal generated by KCl depolarization or acetylcholine propagated through several cell layers by virtue of the regenerative "glutamate-induced glutamate release." Therefore, we suggest that glutamate transporters mediate synchronized elevation of L-glutamate and thereby efficiently downregulate melatonin secretion via previously identified inhibitory metabotropic glutamate receptors in the pineal gland.
    Journal of Neuroscience 11/2008; 28(43):10852-63. · 6.91 Impact Factor
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    ABSTRACT: Protease-activated receptor-2 (PAR-2) is activated when trypsin cleaves its NH(2) terminus to expose a tethered ligand. We previously demonstrated that PAR-2 activates ion channels in pancreatic duct epithelial cells (PDEC). Using real-time optical fluorescent probes, cyan fluorescence protein-Epac1-yellow fluorescence protein for cAMP, PH(PLC-delta1)-enhanced green fluorescent protein for phosphatidylinositol 4,5-bisphosphate, and protein kinase Cgamma (PKCgamma)-C1-yellow fluorescence protein for diacylglycerol, we now define the signaling pathways mediating PAR-2 effect in dog PDEC. Although PAR-2 activation does not stimulate a cAMP increase, it induces phospholipase C to hydrolyze phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate and diacylglycerol. Intracellular Ca(2+) mobilization from inositol 1,4,5-trisphosphate-sensitive Ca(2+) stores and a subsequent Ca(2+) influx through store-operated Ca(2+) channels cause a biphasic increase in intracellular Ca(2+) concentration ([Ca(2+)](i)), measured with Indo-1 dye. Single-cell amperometry demonstrated that this increase in [Ca(2+)](i) in turn causes a biphasic increase in exocytosis. A protein kinase assay revealed that trypsin also activates PKC isozymes to stimulate additional exocytosis. Paralleling the increased exocytosis, mucin secretion from PDEC was also induced by trypsin or the PAR-2 activating peptide. Consistent with the serosal localization of PAR-2, 1 microm luminal trypsin did not induce exocytosis in polarized PDEC monolayers; on the other hand, 10 microm trypsin at 37 degrees C damaged the epithelial barrier sufficiently so that it could reach and activate the serosal PAR-2 to stimulate exocytosis. Thus, in PDEC, PAR-2 activation increases [Ca(2+)](i) and activates PKC to stimulate exocytosis and mucin secretion. These functions may mediate the reported protective role of PAR-2 in different models of pancreatitis.
    Journal of Biological Chemistry 08/2008; 283(27):18711-20. · 4.65 Impact Factor
  • Gastroenterology 01/2008; 134(4). · 12.82 Impact Factor
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    ABSTRACT: Intracellular calcium concentration ([Ca(2+)](i)) is a key factor controlling secretion from various cell types. We investigated how different patterns of [Ca(2+)](i) signals evoke salt secretion via ion transport mechanisms and mucin secretion via exocytosis in dog pancreatic duct epithelial cells (PDEC). Activation of epithelial P2Y(2) receptors by UTP generated two patterns of [Ca(2+)](i) change: 2-10 microm UTP induced [Ca(2+)](i) oscillations, whereas 100 microm UTP induced a sustained [Ca(2+)](i) increase, both in the micromolar range. As monitored by carbon-fibre amperometry, the sustained [Ca(2+)](i) increase stimulated a larger increase in exocytosis than [Ca(2+)](i) oscillations, despite their similar amplitude. In contrast, patch-clamp recordings revealed that [Ca(2+)](i) oscillations synchronously activated a K(+) current as efficiently as the sustained [Ca(2+)](i) increase. This K(+) current was mediated by intermediate-conductance Ca(2+)-activated K(+) channels (32 pS at -100 mV) which were sensitive to charybdotoxin and resistant to TEA. Activation of these Ca(2+)-dependent K(+) channels hyperpolarized the plasma membrane from a resting potential of -40 mV to -90 mV, as monitored in perforated whole-cell configuration, in turn enhancing Na(+)-independent, Cl(-)-dependent and DIDS-sensitive HCO(3)(-) secretion, as monitored through changes in intracellular pH. PDEC therefore encode concentrations of purinergic agonists as different patterns of [Ca(2+)](i) changes, which differentially stimulate K(+) channels, the Cl(-)-HCO(3)(-) exchanger, and exocytosis. Thus, in addition to amplitude, the temporal pattern of [Ca(2+)](i) increases is an important mechanism for transducing extracellular stimuli into different physiological effects.
    The Journal of Physiology 11/2006; 576(Pt 1):163-78. · 4.38 Impact Factor
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    ABSTRACT: Agouti-related protein (AgRP) is an orexigenic peptide which is composed of three parts; the amino (N)-terminus, the middle part, and the carboxyl (C)-terminus. AgRP has been implicated in various cell signaling, but the precise role of each parts are currently unclear. In this study, we have attempted to determine which part of AgRP was critical for insulin secretion. We have found that the C-terminus of AgRP specifically increases the intracellular calcium concentration in pancreatic beta Rin5mf cells in a PLC-dependent manner, whereas the middle part and C-terminus have little effects on calcium release. This calcium response can be observed in the freshly isolated primary beta cells also. Moreover, amperometric measurement reveals that the C-terminus of AgRP increases the rate of exocytosis in Rin5mf cells. We further show that this region of AgRP is responsible for insulin secretion in a PLC-dependent manner. Taken together, these results indicate that the C-terminus of AgRP can participate in the insulin secretion in pancreatic beta cells, through the modulation of calcium release.
    Neuropeptides 09/2005; 39(4):385-93. · 2.07 Impact Factor
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    ABSTRACT: Serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase [AANAT]) is the key enzyme in melatonin synthesis regulated by circadian rhythm. To date, our understanding of the oscillatory mechanism of melatonin has been limited to autoregulatory transcriptional and posttranslational regulations of AANAT mRNA. In this study, we identify three proteins from pineal glands that associate with cis-acting elements within species-specific AANAT 3' untranslated regions to mediate mRNA degradation. These proteins include heterogeneous nuclear ribonucleoprotein R (hnRNP R), hnRNP Q, and hnRNP L. Their RNA-destabilizing function was determined by RNA interference and overexpression approaches. Expression patterns of these factors in pineal glands display robust circadian rhythm. The enhanced levels detected after midnight correlate with an abrupt decline in AANAT mRNA level. A mathematical model for the AANAT mRNA profile and its experimental evidence with rat pinealocytes indicates that rhythmic AANAT mRNA degradation mediated by hnRNP R, hnRNP Q, and hnRNP L is a key process in the regulation of its circadian oscillation.
    Molecular and Cellular Biology 05/2005; 25(8):3232-46. · 5.37 Impact Factor
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    ABSTRACT: Many metabolic factors affect the secretion of insulin from beta-cells and glucagon from alpha-cells of the islets of Langerhans to regulate blood glucose. Somatostatin from delta-cells, considered a local inhibitor of islet function, reduces insulin and glucagon secretion by activating somatostatin receptors in islet cells. Somatostatin secretion from delta-cells is increased by high glucose via glucose metabolism in a similar way to insulin secretion from beta-cells. However, it is unknown how low glucose triggers somatostatin secretion. Because L-glutamate is cosecreted with glucagon from alpha-cells under low-glucose conditions and acts as a primary intercellular messenger, we hypothesized that glutamate signaling triggers the secretion of somatostatin. In this study, we showed that delta-cells express GluR4c-flip, a newly identified splicing variant of GluR4, an (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type ionotropic glutamate receptor of rat. After treatment with L-glutamate, AMPA, or kainate, secretion of somatostatin from isolated islets was significantly stimulated under low-glucose conditions. The glutamate-dependent somatostatin secretion was Ca(2+) dependent and blocked by 6-cyano-7-nitroquinoxaline-2,3-dione. Somatostatin in turn inhibited the secretion of L-glutamate and glucagon from alpha-cells. These results indicate that L-glutamate triggers somatostatin secretion from delta-cells by way of the GluR4c-flip receptor under low-glucose conditions. The released somatostatin may complete the feedback inhibition of alpha-cells. Thus, alpha- and delta-cells may communicate with each other through L-glutamate and somatostatin signaling.
    Diabetes 08/2004; 53(7):1743-53. · 7.90 Impact Factor

Publication Stats

203 Citations
121.10 Total Impact Points

Institutions

  • 2006–2014
    • University of Washington Seattle
      • Department of Physiology and Biophysics
      Seattle, Washington, United States
  • 2002–2013
    • Pohang University of Science and Technology
      • Department of Physics
      Andong, North Gyeongsang, South Korea
  • 2011
    • Trinity Washington University
      Washington, Washington, D.C., United States