Deletion of Kir5.1 Impairs Renal Ability to Excrete Potassium during Increased Dietary Potassium Intake

Abstract

In the distal convoluted tubule, the basolateral inwardly rectifying potassium channel, a heterotetramer of Kir4.1 and Kir5.1, plays an important role in the regulation of potassium excretion by determining the activity of the thiazide-sensitive sodium-chloride cotransporter (NCC). Previous research found that the deletion of Kir4.1 abolishes the effect of dietary potassium intake on NCC and impairs potassium homeostasis. In this study, the authors demonstrate that deleting Kir5.1 abolishes the inhibitory effect of high dietary potassium intake on NCC and impairs the renal ability to excrete potassium during increased dietary potassium intake. Their findings illustrate that like Kir4.1, Kir5.1 is also an essential component of the potassium-sensing mechanism in the distal convoluted tubule, and that Kir5.1 is indispensable for regulation of renal potassium excretion and maintaining potassium homeostasis. The basolateral potassium channel in the distal convoluted tubule (DCT), comprising the inwardly rectifying potassium channel Kir4.1/Kir5.1 heterotetramer, plays a key role in mediating the effect of dietary potassium intake on the thiazide-sensitive NaCl cotransporter (NCC). The role of Kir5.1 (encoded by Kcnj16 ) in mediating effects of dietary potassium intake on the NCC and renal potassium excretion is unknown. We used electrophysiology, renal clearance, and immunoblotting to study Kir4.1 in the DCT and NCC in Kir5.1 knockout ( Kcnj16 −/− ) and wild-type ( Kcnj16 +/+ ) mice fed with normal, high, or low potassium diets. We detected a 40-pS and 20-pS potassium channel in the basolateral membrane of the DCT in wild-type and knockout mice, respectively. Compared with wild-type, Kcnj16 −/− mice fed a normal potassium diet had higher basolateral potassium conductance, a more negative DCT membrane potential, higher expression of phosphorylated NCC (pNCC) and total NCC (tNCC), and augmented thiazide-induced natriuresis. Neither high- nor low-potassium diets affected the basolateral DCT’s potassium conductance and membrane potential in Kcnj16 −/− mice. Although high potassium reduced and low potassium increased the expression of pNCC and tNCC in wild-type mice, these effects were absent in Kcnj16 −/− mice. High potassium intake inhibited and low intake augmented thiazide-induced natriuresis in wild-type but not in Kcnj16 −/− mice. Compared with wild-type, Kcnj16 −/− mice with normal potassium intake had slightly lower plasma potassium but were more hyperkalemic with prolonged high potassium intake and more hypokalemic during potassium restriction. Kir5.1 is essential for dietary potassium’s effect on NCC and for maintaining potassium homeostasis.