Membrane potential of smooth muscle cells of human allantochorial placental vessels

Abstract

The membrane potential of vessel endothelial and smooth muscle cells is central to their function of regulating blood flow. In the present study, the membrane potential (MP) of smooth muscle cells of human placental arteries and veins with or without endothelium is observed. MP is classically obtained using microelectrodes inserted into the smooth muscle cells, either through the endothelium or directly. MP was found to remain stable during 120–140 min and was independent of pH over a wide physiological range. Variation of external temperature induced depolarization at 20°C. Variations in external concentrations of Na + and K + did not influence MP values, while increases in Ca 2+ and Mg 2+ concentrations caused depolarization. The membranes of vascular smooth muscle cells were also depolarized by ouabain. These data suggest that endothelial cell exert a protective effect (release of constricting or relaxing factors) and that MP is regulated, in particular, by lipid-calcium interaction, opening of voltage-dependent Ca 2+-channels and by ATPase.