A Chloride Channel at the Basolateral Membrane of the Distal-convoluted Tubule

Abstract

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 NPo 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, NPo was significantly elevated when the calcium in the pipette was increased from 0 to 5 mM (NPo increased threefold), or pH increased from 6.4 to 8.0 (NPo 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.