The aim of the present study is to examine the role of Kcnj10 (Kir.4.1) in contributing to the basolateral K conductance in the cortical thick ascending limb (cTAL) using Kcnj10+/+ wild-type (WT) and Kcnj10−/− knockout (KO) mice. The patch-clamp experiments detected a 40- and an 80-pS K channel in the basolateral membrane of the cTAL. Moreover, the probability of finding the 40-pS K was significantly higher in the late part of the cTAL close to the distal convoluted tubule than those in the initial part. Immunostaining showed that Kcnj10 staining was detected in the basolateral membrane of the cTAL but the expression was not uniformly distributed. The disruption of Kcnj10 completely eliminated the 40-pS K channel but not the 80-pS K channel, suggesting the role of Kcnj10 in forming the 40-pS K channel of the cTAL. Also, the disruption of Kcnj10 increased the probability of finding the 80-pS K channel in the cTAL, especially in the late part of the cTAL. Because the channel open probability of the 80-pS K channel in KO was similar to those of WT mice, the increase in the 80-pS K channel may be achieved by increasing K channel number. The whole cell recording further showed that K reversal potential measured with 5 mM K in the bath and 140 mM K in the pipette was the same in the WT and KO mice. Moreover, Western blot and immunostaining showed that the disruption of Kcnj10 did not affect the expression of Na-K-Cl cotransporter 2 (NKCC2). We conclude that Kir.4.1 is expressed in the basolateral membrane of cTAL and that the disruption of Kir.4.1 has no significant effect on the membrane potential of the cTAL and NKCC2 expression.

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.