Inwardly rectifying currents in human term placental cells.

Using the whole cell voltage clamp technique, inwardly rectifying currents were observed in most cells isolated from human term placentas. Reversal potentials, estimated by extrapolation, as well as those estimated by tail currents, were found to be between -80mV and -90mV. These potentials are close to the potassium equilibrium potential (theoretical value: -82 mV). In addition, the inwardly rectifying currents were blocked by 1 mM CsCl. The elevation of [K]e increased the current amplitudes. Furthermore, the holding currents were inwardly shifted when the holding potential was kept at -70mV. The extrapolated reversal potentials changed linearly on a semilogarithmic graph with a slope of 57 mV/decade of [K]e. This value is close to the theoretical calculation (58 mV/decade). Consequently, it is suggested from these studies, that inwardly rectifying currents observed in human term placental cells are carried mainly by potassium ions.