NO stimulation of ATP-sensitive potassium channels: Involvement of Ras/mitogen-activated protein kinase pathway and contribution to neuroprotection

ATP-sensitive potassium (K-ATP) channels regulate insulin release, vascular tone, and neuronal excitability. Whether these channels are modulated by NO, a membrane-permeant messenger in various physiological and pathological processes, is not known. The possibility of NO signaling via K-ATP channel modulation is of interest because both NO and K-ATP have been implicated in physiological functions such as vasodilation and neuroprotection. In this report, we demonstrate a mechanism that leads to K-ATP activation via NO/Ras/mitogen-activated protein kinase pathway. By monitoring K-ATP single-channel activities from human embryonic kidney 293 cell-attached patches expressing sulfonylurea receptor 2B and Kir6.2, we found K-ATP stimulation by NO donor Noc-18, a specific NO effect abolished by NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) but not guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). NO stimulation of K-ATP is indirect and requires Ras and mitogen-activated protein kinase kinase activities. Blockade of Ras activation by pharmacological means or by coexpressing either a dominant-negative or an S-nitrosylation-site mutant Ras protein significantly abrogates the effects of NO. Inhibition of mitogen-activated protein kinase kinase abolishes the NO activation of K-ATP but suppression of phosphatidylinositol 3-kinase does not. The NO precursor L-Arg also stimulates K-ATP via endogenous NO synthase and the Ras signaling pathway. In addition, in rat hippocampal neurons, the protective effect of ischemic preconditioning induced by oxygen-glucose deprivation requires K-ATP and NO synthase activity during preconditioning. Thus, neuroprotection caused by NO released during the short episode of sublethal ischemia may be mediated partly by K-ATP stimulation.