Dual effect of nitric oxide on cytosolic Ca2+ concentration and insulin secretion in rat pancreatic β-cells

In isolated rat pancreatic beta-cells, the nitric oxide (NO) donor NOC-7 at 1 muM reduced the amplitude of the oscillations of cytosolic Ca2+ concentration ([Ca2+](c)) induced by 11.1 mM glucose, and at 10 muM terminated them. In the presence of N-G-nitro-L-arginine (L-NNA), however, NOC-7 at 0.5 and 1 muM increased the amplitude of the [Ca2+](c) oscillations, although the NO donor at 10 muM still suppressed them. Aqueous NO solution also had a dual effect on the [Ca2(+)](c) oscillations. The soluble guanylate cyclase inhibitor LY-83583 and the cGMP-dependent protein kinase inhibitor KT5823 inhibited the stimulatory effect of NO, and 8-bromo-cGMP increased the amplitude of the [Ca2+](c) oscillations. Patch-clamp analyses in the perforated configuration showed that 8-bromo-cGMP inhibited whole cell ATP-sensitive K+ currents in the isolated rat pancreatic beta-cells, suggesting that the inhibition by cGMP of ATP-sensitive K+ channels is, at least in part, responsible for the stimulatory effect of NO on the [Ca2+](c) oscillations. In the presence of L-NNA, the glucose-induced insulin secretion from isolated islets was facilitated by 0.5 muM NOC-7, whereas it was suppressed by 10 muM NOC-7. These results suggest that NO facilitates glucose-induced [Ca2+](c) oscillations of beta-cells and insulin secretion at low concentrations, which effects are mediated by cGMP, whereas NO inhibits them in a cGMP-independent manner at high concentrations.