5‐Hydroxytryptamine, angiotensin and bradykinin transiently increase intracellular calcium concentrations and PKC‐α activity, but do not induce mitogenesis in human vascular smooth muscle cells

Abstract

The potent vasoconstrictor substances, 5-hydroxytryptamine (5-HT), angiotensin II (A II), and bradykinin bind to G-protein coupled receptors and activate phospholipase C-beta. Using the Fura-2 technique and microfluorometry we found that all three agonists induce a transient increase in intracellular calcium ([Ca2+]i) by releasing stored calcium in human renal artery smooth muscle cells. Using binding of [3H]-phorbol dibutyrate (PDBu) to quantify membrane-associated protein kinase C (PKC) we also showed that 5-HT, A II and bradykinin induced a rapid but transient translocation of protein kinase C (PKC) to the plasma membrane. The time-course of the rise in [Ca2+]i was similar to that of the increase in [3H]-PDBu binding, suggesting transient activation of the calcium dependent alpha-isoform of PKC. Following prolonged pre-treatment with tetradecanoyl phorbol acetate (100 nmol L-1), which down-regulates PKC-alpha and delta, the angiotensin-induced PKC translocation was lost. 5-HT, A II or bradykinin were unable to increase cell proliferation or act as a co-mitogens with platelet-derived growth factor in human vascular smooth muscle cells. Thus, transient increases in [Ca2+]i or PKC activity by a vasoconstrictor agent are insufficient to cause vascular smooth muscle proliferation.