SWELLING-INDUCED ANION AND CATION CONDUCTANCES IN HUMAN EPIDIDYMAL CELLS

1. Activation of both anion and cation conductances was observed in pr imary cultured human epididymal cells during osmotic swelling under th e patch-clamp whole-cell configuration. The swelling-induced anion con ductance was 25.66+/-4.70 nS and the cation conductance was 7.35+/-1.4 0 nS. The permeability ratio of K+ to Cl- (P-K/P-Cl) was calculated to be 0.40. Known anion or cation channel blockers could inhibit both co nductances simultaneously. 2. When the major permeant ion species in t he pipette and bath solution was Cl-, the mean conductance was found t o be 17.06+/-1.8 nS, significantly smaller than that obtained in the p resence of intracellular K+, 25.66+/-4.70 nS (P < 0.05). No significan t 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 permeabilit y ratios mere calculated to be P-Glut/P-Cl = 0.20 and P-Asp/P-Cl= 0.17 4. The cation conductance was found to be non-selective since its per meability to other cations such as Na+ and choline, an organic compoun d 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 bl ockers. 6. The results of this study suggest that both anion and catio n conductances are activated during cellular swelling, and indicate th e existence of an interdependent relationship between the swelling-ind uced cation and anion conductances. Both swelling-induced cation and a nion conductances are involved in the volume regulatory process and ma y be responsible for transporting amino acids or organic compounds in human epididymal cells.