Role of phosphatidylinositol 3-kinase in acetylcholine-induced dilatation of rat basilar artery

Abstract

Background and Purpose - We tested the hypothesis that activation of phosphatidylinositol (PI) 3-kinase is involved in dilator responses of the basilar artery to acetylcholine in vivo. Methods - Responses of the basilar artery were measured by the cranial window technique in anesthetized rats. To examine the role of PI 3-kinase in acetylcholine-induced calcium signaling, we measured intracellular free calcium concentration ([Ca2+](i)) of cultured rat basilar arterial endothelial cells using a fluorescent calcium indicator, indo 1. Results - Topical application of acetylcholine (10-6, 10-5.5, and 10-5 mol/L) increased the diameter of the basilar artery by 8±1%, 14±2%, and 24±3%, respectively. An inhibitor of PI 3-kinase, wortmannin (10-8 mol/L), did not change the baseline diameter of the artery. In the presence of wortmannin, acetylcholine (10-6, 10-5.5, and 10-5 mol/L) dilated the artery only by 3±2%, 6±2%, and 12±2%, respectively. Thus, wortmannin attenuated acetylcholine-induced dilatation of the basilar artery (P<0.05 versus control). Wortmannin had no effect on dilatation of the artery in response to a nitric oxide donor, sodium nitroprusside. LY294002, another inhibitor of PI 3-kinase, also inhibited dilator response of the basilar artery to acetylcholine. Acetylcholine produced an increase in [Ca2+](i) of the endothelial cells. Genistein, an inhibitor of tyrosine kinase, markedly attenuated acetylcholine-induced calcium influx to the cells; however, wortmannin had no effect on acetylcholine-induced calcium changes. Conclusions - These results suggest that acetylcholine-induced dilatation of the basilar artery is mediated, at least in part, by activation of PI 3-kinase in vivo. Acetylcholine-induced [Ca2+](i) changes of the endothelial cells may not be mediated by activation of the kinase. PI 3-kinase as well as [Ca2+](i) may play an important role in the acetylcholine-induced nitric oxide production of the basilar arterial endothelial cells.