The resting potential of mouse Leydig cells:: Role of an electrogenic Na+/K+ pump

Resting potentials (V-m) were measured in mouse Leydig cells, using the whole-cell patch-clamp technique. In contrast to conventional microelectrode measurements, where a biphasic potential was observed, we recorded a stable V-m around -32.2 +/- 1.2 mV (mean +/- SEM, n = 159), at 25degreesC, and an input resistance larger than 2.7 x 10(9) Omega. Although V-m is sensitive to changes in the extracellular concentrations of potassium and chloride, the relationship between V-m and these ions' concentrations cannot be described by either the Goldman-Hodgkin-Katz or the Nernst equation. Perifusing cells with potassium-free solution or 10(-3) M ouabain induced a marked depolarization averaging 20.1 +/- 3.2 mV (n = 9) and 23.1 +/- 2.8 mV, (n = 7), respectively. Removal of potassium or addition of ouabain with the cell voltage-clamped at its V-m, resulted in an inwardly directed current, due to inhibition of the Na(+)K(+)ATPase. The pump current increased with temperature with a Q(10) coefficient of 2.3 and had an average value of -6.5 +/- 0.4 pA (n = 2 1) at 25degreesC. Vm also varied strongly with temperature, reaching values as low as -9.2 +/- 1.2 mV (n = 22) at 15degreesC. Taking the pump current at 25degreesC and a minimum estimate for the membrane input resistance, we can see that the Na+K+ ATPase could directly contribute with 17.7 mV to the V-m of Leydig cells, which is a major fraction of the -32.2 +/- .2 mV (n = 159) observed.