Role of WNK4 and kidney-specific WNK1 in mediating the effect of high dietary K⁺ intake on ROMK channel in the distal convoluted tubule

Abstract

With-no-lysine kinase 4 (WNK4) and kidney-specific (KS)-WNK1 regulate ROMK (Kir1.1) channels in a variety of cell models. We now explore the role of WNK4 and KS-WNK1 in regulating ROMK in the native distal convoluted tubule (DCT)/connecting tubule (CNT) by measuring tertiapin-Q (TPNQ; ROMK inhibitor)-sensitive K currents with whole cell recording. TPNQ-sensitive K currents in DCT2/CNT of KS- WNK1 and WNK4 mice were significantly smaller than that of WT mice. In contrast, the basolateral K channels (a Kir4.1/5.1 heterotetramer) in the DCT were not inhibited. Moreover, WNK4 mice were hypokalemic, while KS- WNK1 mice had normal plasma K levels. High K (HK) intake significantly increased TPNQ-sensitive K currents in DCT2/CNT of WT and WNK4 mice but not in KS- WNK1 mice. However, TPNQ-sensitive K currents in the cortical collecting duct (CCD) were normal not only under control conditions but also significantly increased in response to HK in KS- WNK1 mice. This suggests that the deletion of KS-WNK1-induced inhibition of ROMK occurs only in the DCT2/CNT. Renal clearance study further demonstrated that the deletion of KS-WNK1 did not affect the renal ability of K excretion under control conditions and during increasing K intake. Also, HK intake did not cause hyperkalemia in KS- WNK1 mice. We conclude that KS-WNK1 but not WNK4 is required for HK intake-induced stimulation of ROMK activity in DCT2/CNT. However, KS-WNK1 is not essential for HK-induced stimulation of ROMK in the CCD, and the lack of KS-WNK1 does not affect net renal K excretion.

ENaC and ROMK channels in the connecting tubule regulate renal K+ secretion

“…The findings were confirmed by Wu et al (2020) , who reported that DCT/CNT cells were more sensitive than those of the CCD to changes in angiotensin II signaling. ROMK currents have also been observed in this segment, and their activity is increased in animals fed a K-rich diet ( Zhang et al, 2017 ; Wu et al, 2018 ).…”

“…The DCT is recognized by the convolutions and, in favorable cases, by an attached thick ascending limb and/or glomerulus. The tubule eventually straightens and narrows abruptly at a point considered to represent the junction between the DCT2 and the CNT ( Nesterov et al, 2012 ; Wu et al, 2018 ). We opened the tubule at various points along its length, both proximal and distal to this narrowing, and made whole-cell recordings under conditions favorable to the detection of ENaC currents.…”

WNK bodies cluster WNK4 and SPAK/OSR1 to promote NCC activation in hypokalemia

“…WNK bodies become prominent when NCCs are activated by dietary K ϩ restriction ( 29), yet genetically engineered models have shown that NCC activity and WNK body formation can be dissociated. For example, NCC activity is high when WNK bodies are absent in mice lacking KS-WNK1 or in models of PHAII due to wnk1 or wnk4 mutations (11,33,36). To date, the relevance of WNK bodies to WNK-SPAK/OSR1 signaling has remained elusive.…”

“…To date, the relevance of WNK bodies to WNK-SPAK/OSR1 signaling has remained elusive. Wu et al (36) provided functional data showing that the inhibition of NCC upon dietary K ϩ loading is blunted in mice lacking KS-WNK1. This observation is consistent with preliminary data provided by Boyd-Shiwarski et al (5), who found that the ability of KS-WNK1deficient mice to reduce NCC phosphorylation in hyperkalemia and to increase NCC phosphorylation in hypokalemia are both compromised.…”

“…Deletion of KS-WNK1 leads to activation of NCC and a mild elevation in blood pressure (11,17). Recently, it has been shown that deletion of KS-WNK1 abrogates the suppression of NCC activity by K ϩ loading (36). In a preliminary report (5), KS-WNK1 deletion blunted NCC activation upon K ϩ deprivation.…”