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Functional and Structural Analysis of ClC-K Chloride Channels Involved in Renal Disease*

S. Waldegger,T. Jentsch

Published 2000 in Journal of Biological Chemistry

ABSTRACT

ClC-K channels belong to the CLC family of chloride channels and are predominantly expressed in the kidney. Genetic evidence suggests their involvement in transepithelial transport of chloride in distal nephron segments; ClC-K1 gene deletion leads to nephrogenic diabetes insipidus in mice, and mutations of the hClC-Kb gene cause Bartter's syndrome type III in humans. Expression of rClC-K1 in Xenopus oocytes yielded voltage-independent currents that were pH-sensitive, had a Br− > NO3 − = Cl− > I− conductance sequence, and were activated by extracellular calcium. A glutamate for valine exchange at amino acid position 166 induced strong voltage dependence and altered the conductance sequence of ClC-K1. This demonstrates that rClC-K1 indeed functions as an anion channel. By contrast, we did not detect currents upon hClC-Kb expression in Xenopus oocytes. Using a chimeric approach, we defined a protein domain that, when replaced by that of rClC-K1, allowed the functional expression of a chimera consisting predominantly of hClC-Kb. Its currents were linear and were inhibited by extracellular acidification. Contrasting with rClC-K1, they displayed a Cl− > Br−> I−> NO3 − conductance sequence and were not augmented by extracellular calcium. Insertion of point mutations associated with Bartter's syndrome type III destroyed channel activity. We conclude that ClC-K proteins form constitutively open chloride channels with distinct physiological characteristics.

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