Effect of cyclic AMP on the calcium-dependent potassium conductances of rat Leydig cells.

Two potassium conductances have been isolated in rat Leydig cells by their sensitivity to cytosolic calcium and to K+ channel blockers. We used the whole-cell configuration of the patch-clamp technique to investigate their sensitivity to cyclic AMP, the main messenger of luteinizing hormone, which stimulates Leydig cell steroidogenesis. The voltage-dependent potassium conductance is not modified by exposing the cell to 1 mM chlorophenylthio-cyclic AMP (CPT-cAMP), a membrane-permeant analogue of cAMP. By contrast, the large, calcium-activated potassium conductance is upregulated by CPT-cAMP. Furthermore, the latter is potentiated by the chloride channel blocker 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid, sodium salt (SITS).