Kir4.1 is involved in Bradykinin‐induced inhibition of NCC and natriuresis

Abstract

Stimulation of type II bradykinin (BK) receptor (BK2R) has been shown to increase renal Na+ excretion. However, the mechanism by which BK stimulates natriuresis is not completely understood. Immunohistochemical study demonstrates that BK2R is highly expressed in both apical and basolateral membrane of Kir4.1 positive tubules including thick ascending limb, distal convoluted tubule (DCT) and cortical collecting duct. The aim of the present study is to explore the role of BK in regulating the basolateral K+ channel and apical Na‐Cl cotransporter (NCC) in the DCT. The single channel patch‐clamp experiments show that application of BK (1–10 μM) inhibited the basolateral 40 pS K+ channel (a Kir4.1/5.1 heterotetramer) and this effect was blocked by BK2R antagonist (HOE140) but not by BK1R antagonist. Whole‐cell recordings have also shown that BK decreased the basolateral K+ conductance of the DCT and depolarized the membrane. To examine the role of Kir4.1 in mediating BK‐induced natriuresis, we performed renal clearance experiment in WT and in kidney‐specific conditional Kir4.1 knockout (Ks‐Kir4.1 KO) mice. Acute application of BK increased urinary Na+ and K+ excretion. However, the BK‐induced natriuretic effect was completely abolished in Ks‐Kir4.1 KO mice. The results strongly suggest that Kir4.1 activity is required for BK‐induced natriuresis. Our previous experiments demonstrated that Kir4.1 plays an important role in determining NCC activity such that the deletion of Kir4.1 completely inhibited NCC in the DCT. To test the hypothesis that BK‐induced inhibition of Kir4.1 may cause the inhibition of NCC thereby increasing Na+ and K+ excretion, we examine the basolateral Kir4.1 activity, the expression of NCC and thiazide‐induced natriuresis in the mice with 3 day infusion of BK by an osmotic pump. The infusion of BK for 3 days significantly decreased the basolateral Kir4.1 conductance and the negativity of the DCT membrane. Western blot showed that infusion of BK decreased the expression of total NCC and phosphorylated NCC. Renal clearance experiments demonstrated that thiazide‐induced natriuresis was blunted in the mice receiving BK infusion, suggesting that BK infusion inhibited NCC function in the DCT. Consequently, mice received BK infusion for 3 days were hypokalemic, presumably due to increasing Na and volume delivery to the collecting duct. We conclude that BK2R plays a role in tonic inhibition of the basolateral Kir4.1 channels in the DCT and that BK‐induced inhibition of NCC is, at least in part, responsible for BK‐induced stimulation of Na excretion. We also conclude that BK‐induced inhibition of Kir4.1 in the DCT is an essential step for the inhibition of NCC.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.