Whole cell patch clamping of ciliary epithelial cells during anisosmotic swelling

Anisosmotic cell swelling triggers a regulatory volume decrease (RVD) in cell lines derived from human nonpigmented ciliary epithelium. Measurements of cell volume have indicated that the RVD reflects activation of K+ and/or Cl- channels. We have begun to characterize the putative channels by whole cell patch clamping. The results obtained by altering the external K+ and Cl- concentrations and by adding 20-50 microM quinidine or 1 mM Ba2+ indicate that K+ conductances contribute substantially and Cl- conductances contribute very little to the total membrane conductance (GT) under baseline isotonic conditions. Reducing the external osmolality by 20-50% reversibly and reproducibly increased GT by an order of magnitude. Data obtained from ion substitutions and the channel blockers quinidine and 5-nitro-2-(3-phenylpropylamino)-benzoate indicate that most of the hypotonicity-induced conductance reflects stationary Cl(-)-channel activity. The contribution of new K(+)-channel activity was small at intracellular free Ca2+ concentrations of 10 or 200 nM. We conclude that the RVD triggered by bath hypotonicity primarily reflects increased Cl(-)-channel activity.