Electrophysiological study of single Leydig cells freshly isolated from rat testis. II. Effects of ionic replacements, inhibitors and human chorionic gonadotropin on a calcium activated potassium permeability.

Changes in the membrane potential of isolated Leydig cells produced by modified ionic solutions were investigated in vitro either by a total change of the bathing medium (procedure P1) or by a flush of the solution around the impaled cell (procedure P2). In standard Earle's solution, the impalement of 198 cells by a glass microelectrode was accompanied by an hyperpolarization (MP1 = -37.6 +/- 0.7 mV) (means +/- S.E.M.) followed by a gradual depolarization to a steady state potential (MP2 = -25.1 +/- 0.6 mV) (Joffre et al. 1984). Experiments with K modified media (P1) showed that MP2, and to a greater extend MP1, were dependent on the external K. A tenfold increase of K decreased MP2 by 16 mV and MP1 by 25 mV. When the extracellular Cl was reduced (P1) by substituting Cl with a less permeant anion, MP2 was unchanged and MP1 was significantly decreased. A transient depolarization of MP2 occurred when a low Cl medium was flushed (P2). An equimolar Na replacement by choline chloride (P1) did not change MP1 or MP2, during the first 10 min. It suppressed MP1 and decreased MP2 after a 15 min exposure. MP1 reappeared and MP2 increased after the restoration of the normal Na solution (P1 and P2). The modification of external Ca from 0 to 3.6 mM (P1) increased both MP1 and MP2. MP1 was never cancelled in 0 mM Ca. In 18 mM Ca, MP1 was suppressed and MP2 decreased. Restoration of 1.8 mM Ca was rapidly accompanied by the MP1 reappearance.(ABSTRACT TRUNCATED AT 250 WORDS)