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Cl^– channels of the distal nephron

Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York

Submitted 9 December 2005 ; accepted in final form 2 May 2006

Cl^– currents were observed under whole cell clamp conditions in cells of the rat cortical collecting duct (CCD), connecting tubule (CNT), and thick ascending limb of Henle's loop (TALH). These currents were much larger in intercalated cells compared with principal cells of the CCD and were also larger in the TALH and in the CNT compared with the CCD. The conductance had no strong voltage dependence, and steady-state currents were similar in inward and outward directions with similar Cl^– concentrations on both sides of the membrane. Current transients were observed, particularly at low Cl^– concentrations, which could be explained by solute depletion and concentration in fluid layers next to the membrane. The currents had a remarkable selectivity among anions. Among halides, Br^– and F^– conductances were only 15% of that of Cl^–, and I^– conductance was immeasurably small. SCN^– and OCN^– conductances were 50%, and aspartate, glutamate, and methanesulfonate conductance was 5% that of Cl^–. No conductance could be measured for any other anion tested, including NO₃^–, HCO₃^–, formate, acetate, or isethionate; NO₃^– and I^– appeared to block the channels weakly. Conductances were diminished by lowering the extracellular pH to 6.4. The properties of the conductance fit best with those of the cloned renal anion channel ClC-K2 and likely reflect the basolateral Cl^– conductances of the cells of these nephron segments.

ClC-K2; anion selectivity; basolateral membrane; intercalated cells

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