Endothelial cell protein kinase G inhibits release of EDHF through a PKG-sensitive cation channel

The release of dilator agents from vascular endothelial cells is modulated by changes in cytosolic Ca2+ concentration ([Ca2+](i)). In this study, we d emonstrate the presence of a Ca2+-permeable cation channel in inside-out me mbrane patches of endothelial cells isolated from small mesenteric arteries . The activity of the channel is increased by KT-5823, a highly selective i nhibitor of protein kinase G (PKG), while it is decreased by direct applica tion of active PKG. Application of KT-5823 induces Ca2+ influx in the endot helial cells isolated from small mesenteric arteries, and it also causes en dothelium-dependent relaxations in isolated small mesenteric arteries. KT-5 823-induced relaxations in small mesenteric arteries are greatly reduced by 35 mM K+ or 50 nM charybdotoxin + 50 nM apamin, suggesting that endotheliu m-derived hyperpolarizing factor (EDHF) is the participating dilator. The i nvolvement of EDHF is further supported by experiments in which the relaxat ions of small mesenteric arteries are shown to be accompanied by membrane r epolarization. These data strongly argue for a major role of a PKG-sensitiv e cation channel in modulating the release of EDHF from endothelial cells i n rat small mesenteric arteries.