Expression and targeting to the plasma membrane of xCIC-K, a chloride channel specifically expressed in distinct tubule segments of Xenopus laevis kidney

ClC-K channels are Cl- channels specifically expressed in vertebrate kidney s. Although their heterologous functional expression is still controversial , indirect evidence points to them as major factors involved in Cl- reabsor ption in the nephron. We cloned xClC-K, an amphibian (Xenopus) homologue of mammalian ClC-K. The cDNA encodes a 77 kDa protein presenting 62% similari ty with human CIC-Kb. The protein is monoglycosylated and is expressed prim arily in the Xenopus kidney. It is localized in the basolateral membranes o f proximal convoluted tubules of the nephron and in the apical region of th e diluting segments. Heterologous expression of xClC-K in HEK-293 cells sho wed that the full-length protein is glycosylated and targeted to the cell m embrane, but no associated Cl- current could be observed with the patch-cla mp recording technique. N-glycosylation of both the native kidney channel a nd the recombinant protein expressed in HEK-293 conferred on them anomalous behaviour in denaturing PAGE, which is indicative of strong interactions a t the extracellular side of the plasma membrane. The expression of ClC-K ch annels in both mesonephric and metanephric kidneys will permit further comp arative physiological studies of Cl- permeabilities at the molecular level.