AN ATP-ACTIVATED CATION CONDUCTANCE IN HUMAN EPIDIDYMAL CELLS

An outwardly rectifying conductance was observed in primary cultured h uman epididymal cells under the patch-clamp whole-cell configuration i n KCl pipette and bath solutions. Removal of Cl- from intracellular an d extracellular solutions did not affect this conductance, but substit ution of K+ with N-methyl-D-glucamine in both solutions completely blo cked the current. The current magnitude was also found to be affected by intracellular but not extracellular K+ concentrations. The conducta nce could be inhibited by the cation channel blockers, barium and tetr aethylammonium chloride. Single-channel recordings from the same cell population also revealed the presence of a conductance of about 150 pS with voltage dependence and blocker sensitivity similar to those obse rved for the whole-cell current. This cation conductance was not affec ted by changes in solution osmolarity but could be activated by extrac ellular ATP. ATP activation of the conductance could be mimicked by io nomycin and inhibited by BAPTA-AM, an agent that suppresses intracellu lar free Ca2+. This ATP-regulated cation conductance may be responsibl e for secreting K+ across the epididymal epithelium, resulting in an o bserved K+ concentration much higher in the lumen of the epididymis th an in the blood.