Functional role of charybdotoxin-sensitive K+ channels in the resting state of dog basilar artery.

To determine the possible role of Ca(2+)-activated K+ (KCa) channels in the regulation of resting tone of cerebral arteries, the effect of agents which interact with these channels on tension and 86Rb efflux was examined in endothelium-denuded strips of dog basilar artery, and data were compared with findings in the mesenteric artery. The basilar artery maintained a myogenic tone; that is, the resting tone decreased when nifedipine was added. The addition of charybdotoxin, a blocker of large conductance KCa channels, caused a concentration-dependent contraction in the basilar artery but not in the mesenteric artery. In strips preloaded with 86Rb, the basal 86Rb efflux rate constant was significantly greater in the basilar artery than in the mesenteric artery. Nifedipine decreased the basal 86Rb efflux rate constant only in the basilar artery. The basal 45Ca influx in the resting state of the basilar artery was significantly increased when compared with the mesenteric artery and this increase in the basilar artery was reduced by nifedipine. The results suggest that the charybdotoxin-sensitive KCa channels regulate the myogenic tone in the resting state of the basilar artery. The activation of KCa channels in the basilar artery appears to be secondary to the increased transmembrane Ca2+ influx probably via the activation of L-type voltage-dependent Ca2+ channels in the resting state of this artery.