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

Abstract

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.

Basolateral Kir4.1 activity in the distal convoluted tubule regulates K secretion by determining NaCl cotransporter activity

“…In addition to cTAL and DCT, immunostaining and the patch-clamp experiments have detected Kir4.1 expression and activity in the basolateral membrane of the CNT and CCD [40*]. Like in the DCT, Kir4.1 interacts with Kir5.1 to form a 40–45 pS inwardly-rectifying K channels in the CNT and CCD [41;42].…”

“…However, experiments performed in p9 c57/bl6 mice have showed that the positive staining of Kir4.1 was limited in the top portion of the renal cortex but was almost absent in the low portion of the renal cortex. Moreover, K channels other than Kir4.1/5.1 heterotetramer were also detected in the basolateral membrane of the CNT and CCD of both adult and p9 neonatal mice [40*]. Therefore, unlike in the DCT, Kir4.1 participates only partially in generating the membrane potential in the CNT and CCD [40].…”

“…Moreover, K channels other than Kir4.1/5.1 heterotetramer were also detected in the basolateral membrane of the CNT and CCD of both adult and p9 neonatal mice [40*]. Therefore, unlike in the DCT, Kir4.1 participates only partially in generating the membrane potential in the CNT and CCD [40]. This notion is suggested by experiments performed in p9 neonatal Kir4.1 knockout mice in which the K reversal potential (an index of the cell membrane potential) in the CNT/CCD was only modestly depolarized in the knockout mice in comparison to those of WT littermates.…”

“…Experiments performed in global Kir4.1 knockout mice have shown that the depletion of Kir4.1 stimulates the expression of ENaC-β, γ subunits and cleaved ENaC-α in the collecting duct [40*]. The upregulation of ENaC expression may explain the fact why patients with EAST/SeSAME syndrome have a modest phenotype of salt wasting despite of the inhibition of Na transport in the DCT [23].…”

Essential role of Kir5.1 channels in renal salt handling and blood pressure control

“…The renal phenotype of these mutations includes salt wasting, hypomagnesemia, metabolic alkalosis, and hypokalemia. Experiments with the Kcnj10-knockout (Kcnj10 -/-) mice revealed that the lack of K ir 4.1 resulted in an early postnatal mortality, decreased expression of the NCC (23), and increased levels of β and γ subunits of the epithelial sodium channel (ENaC) (24). Targeted disruption of the Kcnj16 gene in mice caused hypokalemic, hyperchloremic metabolic acidosis with hypercalciuria (25).…”