Activation of both anion and cation conductances was observed in primary cultured human epididymal cells during osmotic swelling under the patch-clamp whole-cell configuration. The swelling-induced anion conductance was 25.66 +/- 4.70 nS and the cation conductance was 7.35 +/- 1.40 nS. The permeability ratio of K+ to Cl- (PK/PCl) was calculated to be 0.40. Known anion or cation channel blockers could inhibit both conductances simultaneously. 2. When the major permeant ion species in the pipette and bath solution was Cl-, the mean conductance was found to be 17.06 +/- 1.8 nS, significantly smaller than that obtained in the presence of intracellular K+, 25.66 +/- 4.70 nS (P < 0.05). No significant current activation was observed when solutions containing only K+ as the permeant ion were used. 3. When the anionic amino acids glutamate and aspartate were used to replace extracellular Cl-, the permeability ratios were calculated to be PGlut/PCl = 0.20 and PAsp/PCl = 0.17. 4. The cation conductance was found to be non-selective since its permeability to other cations such as Na+ and choline, an organic compound highly concentrated in epididymal fluid, was similar to that of K+. 5. Regulatory volume decrease (RVD) was observed after initial osmotic swelling; this could be inhibited by either anion or cation channel blockers. 6. The results of this study suggest that both anion and cation conductances are activated during cellular swelling, and indicate the existence of an interdependent relationship between the swelling-induced cation and anion conductances. Both swelling-induced cation and anion conductances are involved in the volume regulatory process and may be responsible for transporting amino acids or organic compounds in human epididymal cells.
