Lachheb S, Cluzeaud F, Bens M, Genete M, Hibino H, Lourdel S, Kurachi Y, Vandewalle A, Teulon J, Paulais M. Kir4.1/Kir5.1 channel forms the major K ϩ channel in the basolateral membrane of mouse renal collecting duct principal cells. ϩ channels in the basolateral membrane of mouse cortical collecting duct (CCD) principal cells were identified with patch-clamp technique, real-time PCR, and immunohistochemistry. In cell-attached membrane patches, three K ϩ channels with conductances of ϳ75, 40,

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... d 20 pS were observed, but the K ϩ channel with the intermediate conductance (40 pS) predominated. In inside-out membrane patches exposed to an Mg 2ϩ -free medium, the current-voltage relationship of the intermediate-conductance channel was linear with a conductance of 38 pS. Addition of 1.3 mM internal Mg 2ϩ had no influence on the inward conductance (G in ϭ 35 pS) but reduced outward conductance (Gout) to 13 pS, yielding a Gin/Gout of 3.2. The polycation spermine (6 ϫ 10 Ϫ7 M) reduced its activity on inside-out membrane patches by 50% at a clamp potential of 60 mV. Channel activity was also dependent on intracellular pH (pH i): a sigmoid relationship between pHi and channel normalized current (NPo) was observed with a pK of 7.24 and a Hill coefficient of 1.7. By real-time PCR on CCD extracts, inwardly rectifying K ϩ (Kir)4.1 and Kir5.