In isolated rat pancreatic β-cells, the nitric oxide (NO) donor NOC-7 at 1 μM reduced the amplitude of the oscillations of cytosolic Ca²⁺ concentration ([Ca²⁺]_c) induced by 11.1 mM glucose, and at 10 μM terminated them. In the presence of N ^G-nitro-l-arginine (l-NNA), however, NOC-7 at 0.5 and 1 μM increased the amplitude of the [Ca²⁺]_c oscillations, although the NO donor at 10 μM 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 β-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 ofl-NNA, the glucose-induced insulin secretion from isolated islets was facilitated by 0.5 μM NOC-7, whereas it was suppressed by 10 μM NOC-7. These results suggest that NO facilitates glucose-induced [Ca²⁺]_c oscillations of β-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.