Cl−and K+conductances activated by cell swelling in primary cultures of rabbit distal bright convoluted tubules

Ionic currents induced by cell swelling were characterized in primary cultures of rabbit distal bright convoluted tubule (DCTb) by the whole cell patch-clamp technique. Cl−currents were produced spontaneously by whole cell recording with an isotonic pipette solution or by exposure to a hypotonic stress. Initial Cl−currents exhibited outwardly rectifying current-voltage relationship, whereas steady-state currents showed strong decay with depolarizing pulses. The ion selectivity sequence was I−= Br−> Cl−≫ glutamate. Currents were inhibited by 0.1 mM 5-nitro-2-(3-phenylpropylamino)benzoic acid and 1 mM 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid and strongly blocked by 1 mM diphenylamine-2-carboxylate. Currents were insensitive to intracellular Ca2+but required the presence of extracellular Ca2+. They were not activated in cells pretreated with 200 nM staurosporine, 50 μM LaCl3, 10 μM nifedipine, 100 μM verapamil, 5 μM tamoxifen, and 50 μM dideoxyforskolin. Staurosporine, tamoxifen, verapamil, or the absence of external Ca2+was without effect on the fully developed Cl−currents. Osmotic shock also activated K+currents in Cl−-free conditions. These currents were time independent, activated at depolarized potentials, and inhibited by 5 mM BaCl2. The activation of Cl−and K+currents by an osmotic shock may be implicated in regulatory volume decrease in DCTb cells.