Effect of atrial natriuretic polypeptide on angiotensin II-induced increase of cytosolic free calcium in cultured smooth muscle cells.

We investigated the effects of angiotensin II (ANG II) and synthetic atrial natriuretic polypeptide (ANP) on cytosolic free calcium concentration [( Ca2+]i) of cultured rat vascular smooth muscle cells. Incubation with ANP alone showed little or no change in [Ca2+]i, whereas ANG II alone increased [Ca2+]i in a dose-dependent manner up to 164%, compared with basal levels of 253 +/- 17 nmol/l (mean +/- s.e.m.). Simultaneous addition of 10 nmol/l ANG II and varying concentrations of ANP produced a reduction in the ANG II-induced increase in [Ca2+]i. These data suggest that the vasorelaxant effect of ANP is at least partly mediated by changes in [Ca2+]i.