Disruption of KCNJ10 (Kir4.1) stimulates the expression of ENaC in the collecting duct

Kcnj10 encodes the inwardly rectifying K⁺ channel 4.1 (Kir4.1) and is expressed in the basolateral membrane of late thick ascending limb, distal convoluted tubule (DCT), connecting tubule (CNT), and cortical collecting duct (CCD). In the present study, we perform experiments in postneonatal day 9 Kcnj10^−/− or wild-type mice to examine the role of Kir.4.1 in contributing to the basolateral K⁺ conductance in the CNT and CCD, and to investigate whether the disruption of Kir4.1 upregulates the expression of the epithelial Na⁺ channel (ENaC). Immunostaining shows that Kir4.1 is expressed in the basolateral membrane of CNT and CCD. Patch-clamp studies detect three types of K⁺ channels (23, 40, and 60 pS) in the basolateral membrane of late CNT and initial CCD in wild-type (WT) mice. However, only 23- and 60-pS K⁺ channels but not the 40-pS K⁺ channel were detected in Kcnj10^−/− mice, suggesting that Kir.4.1 is a key component of the 40-pS K⁺ channel in the CNT/CCD. Moreover, the depletion of Kir.4.1 did not increase the probability of finding the 23- and 60-pS K⁺ channel in the CNT/CCD. We next used the perforated whole cell recording to measure the K⁺ reversal voltage in the CNT/CCD as an index of cell membrane potential. Under control conditions, the K⁺ reversal potential was -69 mV in WT mice and -61 mV in Kcnj10^−/− mice, suggesting that Kir4.1 partially participates in generating membrane potential in the CNT/CCD. Western blotting and immunostaining showed that the expression of ENaCβ and ENaCγ subunits from a renal medulla section of Kcnj10^−/− mice was significantly increased compared with that of WT mice. Also, the disruption of Kir4.1 increased aquaporin 2 expression. We conclude that Kir4.1 is expressed in the CNT and CCD and partially participates in generating the cell membrane potential. Also, increased ENaC expression in medullary CD of Kcnj10^−/− mice is a compensatory action in response to the impaired Na⁺ transport in the DCT.