Spatial changes of [Ca2+]i and contraction caused by phorbol esters in vascular smooth muscle cells.

Abstract

In A7r5 smooth muscle cell suspensions, 12-deoxyphorbol 13-isobutyrate (DPB) and phorbol 12,13-dibutyrate (PDB), active phorbol esters for protein kinase C (PKC), increased the intracellular Ca2+ concentration ([Ca2+]i), but 4 alpha-PDB, an inactive phorbol ester, did not. Digital images of the fura 2 fluorescence from single cells revealed that DPB caused elevation of Ca2+ in localized peripheral regions, followed by expansion of this elevated Ca2+ level throughout the cytoplasm. High K+ also induced a dynamic change of [Ca2+]i. DPB and high K+ increased the wrinkles and distortions in the flexible growth surface beneath the cells. In Ca(2+)-depleted media, DPB did not affect [Ca2+]i but substantially increased wrinkles. The increase could be eliminated by staurosporine, a specific inhibitor of PKC. DPB increased the particulate PKC activity in a concentration-dependent manner. These results suggest that PKC activation induces cellular contractions through two distinct mechanisms, one dependent on and another independent of the [Ca2+]i increase.