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(−) ∼ NO(3) (−) > 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.