Characterization of a swelling-induced chloride conductance in cultured rat epididymal cells

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Abstract
Swelling-induced Cl- conductance in cultured rat epididymal cells was characterized using whole cell patch-clamp techniques. Activation of whole cell current with an outwardly rectifying current-potential relationship was observed in cells exposed to hyposmotic solutions. This current was determined, from the observed current-reversal potentials at different Cl- concentrations, to be Cl- selective. The anion selectivity sequence of the swelling-induced Cl- conductance was I- approximately NO3- approximately Br- > Cl- > 2-(N-morpholino)ethanesulfonic acid. The swelling-induced Cl- conductance was reversibly inhibited by different Cl- channel blockers. Unlike diphenylamine-2-carboxylate or 5-nitro-2-(3-phenylpropylamino)-benzoate, which showed voltage-independent blockade, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid showed a marked voltage-dependent blockade of the volume-sensitive Cl- current, with a greater effect at depolarizing voltages. The swelling-induced Cl- conductance appeared to be different from the Ca(2+)- or adenosine 3',5'-cyclic monophosphate-activated Cl- conductances on the basis of the following observations: 1) swelling-induced current activation was seen even in the presence of kinase inhibitor (H-8) or absence of external free Ca2+, and 2) further increase in current activation could be produced by swelling after Ca(2+)- or adenosine 3',5'-cyclic monophosphate-induced current activation. The swelling-induced Cl- conductance may be involved in regulating epithelial cell volume as well as serving other important epididymal functions such as facilitating transepithelial secretion of organic compounds.

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