Role of phosphoinositide 3-kinase {alpha}, protein kinase C, and L-type Ca2+ channels in mediating the complex actions of angiotensin II on mouse cardiac contractility.

Although angiotensin II (Ang II) plays an important role in heart disease associated with pump dysfunction, its direct effects on cardiac pump function remain controversial. We found that after Ang II infusion, the developed pressure and +dP/dt(max) in isolated Langendorff-perfused mouse hearts showed a complex temporal response, with a rapid transient decrease followed by an increase above baseline. Similar time-dependent changes in cell shortening and L-type Ca(2+) currents were observed in isolated ventricular myocytes. Previous studies have established that Ang II signaling involves phosphoinositide 3-kinases (PI3K). Dominant-negative inhibition of PI3Kalpha in the myocardium selectively eliminated the rapid negative inotropic action of Ang II (inhibited by approximately 90%), whereas the loss of PI3Kgamma had no effect on the response to Ang II. Consistent with a link between PI3Kalpha and protein kinase C (PKC), PKC inhibition (with GF 109203X) reduced the negative inotropic effects of Ang II by approximately 50%. Although PI3Kalpha and PKC activities are associated with glycogen synthase kinase-3beta and NADPH oxidase, genetic ablation of either glycogen synthase kinase-3beta or p47(phox) (an essential subunit of NOX2-NADPH oxidase) had no effect on the inotropic actions of Ang II. Our results establish that Ang II has complex temporal effects on contractility and L-type Ca(2+) channels in normal mouse myocardium, with the negative inotropic effects requiring PI3Kalpha and PKC activities.