A Chloride Channel at the Basolateral Membrane of the Distal-convoluted Tubule : a Candidate ClC-K Channel

The distal-convoluted tubule (DCT) of the kidney absorbs NaCl mainly via an Na⁺-Cl⁻ cotransporter located at the apical membrane, and Na⁺, K⁺ ATPase at the basolateral side. Cl⁻ transport across the basolateral membrane is thought to be conductive, but the corresponding channels have not yet been characterized. In the present study, we investigated Cl⁻ channels on microdissected mouse DCTs using the patch-clamp technique. A channel of ∼9 pS was found in 50% of cell-attached patches showing anionic selectivity. The NP_o in cell-attached patches was not modified when tubules were preincubated in the presence of 10⁻⁵ M forskolin, but the channel was inhibited by phorbol ester (10⁻⁶ M). In addition, NP_o was significantly elevated when the calcium in the pipette was increased from 0 to 5 mM (NP_o increased threefold), or pH increased from 6.4 to 8.0 (NP_o increased 15-fold). Selectivity experiments conducted on inside-out patches showed that the Na⁺ to Cl⁻ relative permeability was 0.09, and the anion selectivity sequence Cl⁻ ∼ I⁻> Br⁻ ∼ NO₃⁻ > F⁻. Intracellular NPPB (10⁻⁴ M) and DPC (10⁻³ M) blocked the channel by 65% and 80%, respectively. The channel was inhibited at acid intracellular pH, but intracellular ATP and PKA had no effect. ClC-K Cl⁻ channels are characterized by their sensitivity to the external calcium and to pH. Since immunohistochemical data indicates that ClC-K2, and perhaps ClC-K1, are present on the DCT basolateral membrane, we suggest that the channel detected in this study may belong to this subfamily of the ClC channel family.