INVOLVEMENT OF EXTERNAL POTASSIUM IN MEMBRANE-POTENTIAL OF SMOOTH-MUSCLE CELLS OF HUMAN ALLANTOCHORIAL PLACENTAL VESSELS

The membrane potential (Um) of smooth muscle cells of human placental vessels is observed in survival medium with varying K+ concentration. In a K+-free medium, the membrane is hyperpolarized, whereas from 8 mM K+ in the medium, a depolarization is observed. There is a linear cor relation between potential variation and [K+](0) (r = 0.98) with a slo pe of 0.412 +/- 0.093 mV/mM K+. Moreover, a K+ depolarization followed by a rinsing indicates the membrane of smooth muscle cells is predepo larized in normal medium. These results show the implication of extern al K+ in the membrane potential level and induce the presence of delay ed rectifier K+ channels and the absence of inward rectifier K+ channe ls in the membrane of smooth muscle cells of human placental vessels. (C) 1998 Elsevier Science S.A.