Expression of TWIK-1, a novel weakly inward rectifying potassium channel in rat kidney

Several K+ conductances have been identified in the kidney, with specific p roperties and localization in distinct cell types and membrane domains. On the other hand, several K+ channels have been characterized at the molecula r level. By immunolocalization, we show that a new inward rectifying K+ cha nnel, TWIK-1, is specifically expressed in distinct tubular segments and ce ll types of the rat kidney. In the proximal tubule, TWIK-1 prevails in the initial portions (convoluted part), where it is restricted to the apica (br ush-border) membrane. In the collecting duct, immunofluorescence was intrac ellular or confined to the apical membrane and restricted to intercalated c ells, i.e., in cells lacking aquaporin-2, as shown by double immunofluoresc ence. TWIK was also expressed in medullary and cortical parts of the thick limb of the loop of Henle, identified with an anti-Tamm-Horsfall protein an tibody (double immunofluorescence). The intensity of TWIK-1 immunolabeling was unchanged in rats fed a low-Na+ or a low-K+ diet. Because TWIK-1 shares common properties with the low-conductance apical K+ channel of the collec ting duct, we propose that it could play a role in K+ secretion, complement ary to ROMK, another recently characterized K+ channel located in principal cells of the cortical collecting duct and in the loop of Henle.