Nicorandil enhances the effect of endothelial nitric oxide under hypoxia-reoxygenation : Role of the KATP channel

Nicorandil increased the anti-platelet aggregation activity of endothelial cells when endothelial cells were exposed to hypoxia-reoxygenation conditions. However, nicorandil (0.1-10 muM) did not inhibit platelet aggregation directly. The mechanism by which nicorandil increases the anti-aggregation activity of hypoxia-reoxygenation treated endothelial cells was investigated. The effect of nicorandil was observed even in indomethacin-treated endothelial cells, but the effect was eliminated by treating endothelial cells with N(G)-nitro-l-arginine methyl ester (L-NAME). This indicates that nicorandil enhances the anti-aggregation activity of endothelial nitric oxide (NO). Nicorandil did not increase the anti-aggregation activity of endothelial NO when endothelial cells were pre-treated with superoxide dismutase or 4-(2-aminophenyl)-benzenesulfonyl fluoride, an inhibitor of NADPH oxidase. Nicorandil dose-dependently inhibited the reactive oxygen species generation induced by an oxidative stress in endothelial cells. The effect of nicorandil on anti-aggregation activity was abrogated by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker. Pinacidil, a K(ATP) channel opener, also enhanced the anti-aggregation activity of endothelial NO. This effect was similarly abrogated by glibenclamide. These results suggest that nicorandil may inhibit the generation of superoxide (O(2)(-)) from hypoxia-reoxygenation treated endothelial cells through activation of the K(ATP) channel, and that nicorandil may prevent the disappearance of endothelial NO by O(2)(-).