AIMTo explore the effects of sinomenine(Sin) on intracellular free calcium ([Ca2+]i) and the activity of PKC (protein kinase C) of the cultured aortic vascular smooth muscle cells (VSMC) during ischemia and hypoxia.

METHODSThe effect of Sin on changes in [Ca2+]i were determined in cultured rabbit VSMC after exposure to high K+, norepinephrine (NE) and caffeine (Caf). Fluorescent Ca2+ -indicater fura-2/AM was used. The effects of Sin were compared with that of verapamil (Ver). The hypoxia model was made, then the activity of PKC was measured by y scintillation counting instrument.

RESULTSSin (10 x 10(-6) mol x L(-1), 3 x 10(-5) mol x L(-1) 10(-4) mol x L(-1)) inhibited the elevation of [Ca2+]i induced by high K+ -depolarization in a concentration dependent manner. In addition, Sin inhibited the elevation of [Ca2+]i induced by NE in the presence of extracellular Ca2+. In the absence of extracellular Ca2+, Sin (3 x 10(-5) mol.L(-1)) also had no blocking effect on the NE-induced [Ca2+]i increase. It was found that the activity of PKC treated with Sin in VSMC cytoplasm and cell membrane in normal condition increased, the activity of PKC in cytoplasm in ischemia and hypoxia situation increased, but the activity of PKC in cell membrane decreased. When VSMC was treated with Sin, the activity of PKC in cytoplasm decreased and that of cell membrane increased.

CONCLUSIONThe results suggest that Sin might decrease the[Ca2+] i of VSMC by blocking both VDC and ROC, could regulate the PKC activities induced by ischemia and hypoxia.