Kir5.1 regulates Kir4.2 expression and is a key component of the 50-pS inwardly rectifying potassium channel in basolateral membrane of mouse proximal tubules.

Kir5.1 encoded by is an inwardly rectifying K channel subunit, and it possibly interacts with Kir4.2 subunit encoded by for assembling a Kir4.2/Kir5.1 heterotetramer in the basolateral membrane of mouse proximal tubule. We now used patch clamp technique to examine basolateral K channels of mouse proximal tubule (PT) and an immunoblotting/immunofluorescence (IF) staining microscope to examine Kir4.2 expression in wild-type and Kir5.1-knockout mice. IF staining shows that Kir4.2 was exclusively expressed in the proximal tubule, whereas Kir5.1 was expressed in the proximal tubule and distal nephrons including distal convoluted tubule. Immunoblotting showed that the expression of Kir4.2 monomer was lower in Kir5.1-knockout mice than that in the wild-type mice. In contrast, Kir4.1 monomer expression was increased in Kir5.1 knockout mice. IF images further demonstrated that the basolateral membrane staining of Kir4.2 was significantly decreased in Kir5.1 knockout mice. This is in sharp contrast to Kir4.1, which also interacts with Kir5.1 in the distal nephron, and IF images show that Kir4.1 membrane expression was still visible and unchanged in Kir5.1 knockout mice. The single channel recording detected a 50-pS inwardly rectifying K channel, presumably a Kir4.2/Kir5.1 heterotetramer, in the basolateral membrane of the proximal tubule of Kir5.1 wild-type mice. However, this 50-pS K channel was completely absent in the basolateral membrane of the proximal tubule of Kir5.1 knockout mice. Moreover, the membrane potential of the proximal tubule was less negative in Kir5.1 knockout mice than wild-type mice. We conclude that Kir5.1 is essential for assembling basolateral 50-pS K channel in proximal tubule and that deletion of Kir5.1 decreased Kir4.2 expression in the proximal tubule thereby decreasing the basolateral K conductance and the membrane potentials. Our study provides direct evidence for the notion that Kir5.1 is a key component of a 50-60 pS inwardly-rectifying-K channel, a main type K channel in the basolateral-membrane of PT. Also, we demonstrate that deletion of Kir5.1 decreased Kir4.2 protein expression including the basolateral-membrane in PT. Finally, depolarization of PT-membrane- potential in Kir5.1-knockout mice suggests that Kir4.2 alone is not able to sustain basolateral K conductance of the PT in the absence of Kir5.1.