Characterization of gap junctions between pairs of Leydig cells from mouse testis

Leydig cells are coupled in vivo by numerous gap junctions. In vivo and in vitro cells were immunolabeled by connexin 43 (Cx43) but not by Cx26 or Cx32 antibodies; immunoblotting confirmed specificity of Cx43 labeling. Pairs of Leydig cells dissociated from mouse testis were studied by dual whole cell voltage clamp, and a high incidence of dye (n = 20) and electrical coupling (n = 60; > 90%) was found. Coupling coefficients were near 1 and junctional conductance (gj) averaged 7.2 +/- 1.2 nS (SE, n = 40). Large transjunctional voltage (Vj) decreased gj; currents decayed exponentially with time constants of seconds that decreased at greater Vj. The residual conductance at large Vj was at least approximately 40% of the initial conductance. Exposure of cell pairs to saline solutions saturated with CO2 (n = 15) or containing 2 mM halothane (n = 15) or 3.5 mM heptanol (n = 15) rapidly and reversibly reduced gj. In eight cell pairs, gating of single junctional channels was observed during halothane-induced reduction in gj. Most gating events at Vj < 40 mV were fit by a Gaussian distribution with a mean of approximately 100 pS. With Vj > 40 mV, smaller transitions of approximately 30 pS were also recorded, and the frequency and duration of the approximately 100-pS transitions decreased. Also, approximately 70-pS transitions between 30- and 100-pS conductances were observed in the absence of 70-pS transitions to or from the baseline, indicating that the 30-pS conductance was a substate induced by large Vj.