Enhanced Ca2+-dependent activation of phosphoinositide 3-kinase class IIα isoform-Rho axis in blood vessels of spontaneously hypertensive rats.

Rho-mediated inhibition of myosin light chain (MLC) phosphatase (MLCP), together with Ca(2+)-dependent MLC kinase activation, constitutes the major signaling mechanisms for vascular smooth muscle contraction. We recently unveiled the involvement of Ca(2+)-induced, phosphoinositide 3-kinase (PI3K) class IIα isoform (PI3K-C2α)-dependent Rho activation and resultant Rho kinase-dependent MLCP suppression in membrane depolarization- and receptor agonist-induced contraction. It is unknown whether Ca(2+)- and PI3K-C2α-dependent regulation of MLCP is altered in vascular smooth muscle of hypertensive animals and is involved in hypertension. Therefore, we studied the role of the Ca(2+)-PI3K-C2α-Rho-MLCP pathway in spontaneously hypertensive rats (SHRs). PI3K-C2α was readily detected in various vascular beds of Wistar-Kyoto rats and activated by high KCl. High KCl also stimulated vascular Rho activity and phosphorylation of the MLCP regulatory subunit MYPT1 at Thr(853) in a PI3K inhibitor wortmannin-sensitive manner. In mesenteric and other vessels of SHRs at the hypertensive but not the prehypertensive stage, the activity of PI3K-C2α but not class I PI3K p110α was elevated with concomitant rises of Rho activity and Thr(853)-phosphorylation of MYPT1, as compared with normotensive controls. Infusion of the Ca(2+) channel antagonist nicardipine reduced blood pressure with suppression of vascular activity of PI3K-C2α-Rho and phosphorylation of MYPT1 in hypertensive SHRs. Infusion of wortmannin lowered blood pressure with inhibition of PI3K-C2α-Rho activities and MYPT1 phosphorylation in hypertensive SHRs. These observations suggest that an increased activity of the Ca(2+)-PI3K-C2α-Rho signaling pathway with resultant augmented MLCP suppression contributes to hypertension in SHRs. The Ca(2+)- and PI3K-C2α-dependent Rho stimulation in vascular smooth muscle may be a novel, promising target for treating hypertension.