Physiological role of NO produced by constitutive NO synthase in pancreatic islet of Langerhans

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METHODS: Pancreatic islets of Langerhans and β cells were isolated from male Wistar rats (9-12 weeks old) by collagenase digestion technique. (1) Double immunostaining with antiserum to NOS1 or NOS3 and that to glucagon, insulin, somatostatin, or pancreatic polypeptide was performed in the isolated islets, and the fluorescent images were analyzed in a confocal laser scanning microscope. (2) The production of NO was measured with the fluorescent NO indicator DAF-2 DA in a confocal laser scanning microscope. (3) [Ca^<2+>]i was measured in fura-PE3-loaded β cells by Argus-50/CA system. (4) The secretion of insulin from isolated islets was measured by the batch incubation method and EIA. (5) ATP-sensitive K^+ currents were measured by the patch clamp method.RESULTS AND DISCUSSION: (1) Double immunostaining showed that both NOS1- and NOS3-immunoreactivity are present in rat β celles. (2) Glucose produced NO in the β cells in a concentration-dependent manner. (3) In the presence of L-NNA, the NO donor NOC7 at 0.5 and 1.0 μM increased the amplitude of [Ca^<2+>]i oscillations induced by 11.1 mM glucose, and at 10 μM terminated them. A soluble guanylyl cyclase inhibitor suppressed the stimulatory action of NOC7 at low concentrations, whereas it did not affect the inhibitory one at high concentrations, suggesting that the former is mediated by cGMP but the latter is not. (4) Insulin secretion induced by 11.1 mM glucose was facilitated by 0.5 μM NOC7, whereas it was suppressed by 10 μM NOC7.CONCLUSION: NO is an endogenous regulator of insulin secretion, which facilitates and inhibits glucose-induced insulin secretion at low and high concentrations, respectively