MEMBRANE-POTENTIAL OF SMOOTH-MUSCLE CELLS OF HUMAN ALLANTOCHORIAL PLACENTAL VESSELS

The membrane potential of vessel endothelial and smooth muscle cells i s central to their function of regulating blood flow. In the present s tudy, the membrane potential (MP) of smooth muscle cells of human plac ental arteries and veins with or without endothelium is observed. MP i s 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 de polarization at 20 degrees C. Variations in external concentrations of Na+ and K+ did not influence MP values, while increases in Ca2+ and M g2+ concentrations caused depolarization. The membranes of vascular sm ooth muscle cells were also depolarized by ouabain. These data suggest that endothelial cells exert a protective effect (release of constric ting or relaxing factors) and that MP is regulated, in particular, by lipid-calcium interaction, opening of voltage-dependent Ca2+-channels and by ATPase.