Dependence of membrane potential on Ca2+ transport in cultured cytotrophoblasts of human immature placentas.
The electrical membrane properties of cultured human cytotrophoblast were examined by means of a standard electrophysiological technique. The mean values of the membrane potential (Rm) and the membrane resistance in a physiological medium were around -49 mV and 12 M omega , respectively. The membrane potential was dependent, to a large extent, on the external Ca2+ concentration ([Ca2+]o). Deprivation of external Ca2+ reduced membrane potential to about -20 mV, and an increase in [Ca2+]o caused a hyperpolarization in a saturable manner. The Ca2+-dependency of membrane potential was affected remarkably by [K+]o, but not by [Na+]o or [Cl-]o. The intracellular Ca2+ injection hyperpolarized the membrane in a Ca2+-free medium. A Ca2+ channel blocker, verapamil, completely abolished the Ca2+-dependent Em. The Ca2+-dependent Em was also suppressed by cooling or by the application of metabolic inhibitors. It is suggested that the Ca2+-dependent Em in cultured human cytotrophoblast is caused by a Ca2+ influx which, in turn, increases the K+ conductance of the cell membrane, presumable due to stimulation of Ca2+-activated K+ channel.
D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D013696:Temperature; D014327:Trophoblasts / Q000378:metabolism*
D002118:Calcium