Transient Ca2+-channel current characterized by a low-threshold voltage in zona glomerulosa cells of rat adrenal cortex.

Voltage-gated Ca2+-current was identified in single isolated cells of the zona glomerulosa of adrenal cortex and its properties were studied by the "tight-seal" whole cell recording technique. The Ca2+ channel current was dissected from the net current by dialyzing the cells with ScCL. The identified Ca2+-current was found to be activated by a relatively small depolarization only when the cells were held at a large negative holding potential, but it was inactivated within 10-30 ms. The time course of activation and inactivation was voltage-dependent and become faster when the amplitude of depolarization was increased. The transmembrane potential of the glomerulosa cells was highly sensitive to [K+]e, the slope of the potential change per tenfold change in [K+]e being 48 mV. An increase in [K+]e from 4.7 to 10 mM induce a membrane depolarization by 15 mV, which was sufficient to cause the membrane to reach the threshold potential (-60 mV) for activation of the Ca2+-current at physiological concentration of [Ca2+]e (2.5 mM-CaCl2). The observed properties of the Ca2+-current and K+-dependence of the membrane potential may give reasonable explanation for the mechanism of Ca2+-uptake and consequent aldosterone secretion induced by a small increase in [K+]e, which is known to be one of the major stimulations for aldosterone secretion.