Kir4.1/Kir5.1 Activity in the DCT is Essential for Angiotensin II Induced Stimulation of Thiazide‐Sensitive NCC Expression/Activity.

Abstract

BackgroundAngiotensin II has been shown to stimulate thiazide‐sensitive Na‐Cl cotransport (NCC) by modulating with‐no‐lysine kinase (WNK) activity. WNK is responsible for the phosphorylation of ste20‐proline‐alanine‐rich protein kinase (SPAK) which regulates NCC activity by the phosphorylation. The basolateral Kir4.1/Kir5.1 channel activity in the DCT plays a role in the regulation of WNK‐SPAK activity by affecting the intracellular Cl concentrations. The aim of the present study is to examine whether Kir4.1/Kir5.1 channel activity in the DCT is required for the effect of angiotensin II on NCC.MethodsWe have used the patch‐clamp methods to examine the effect of angiotensin II on the basolateral K (Kir4.1/Kir5.1) channel activity of the DCT and DCT membrane potential. We also employed immunoblotting to examine the expression of phospho‐NCC (pNCC) and total NCC (tNCC), and used renal clearance method to measure thiazide‐sensitive renal sodium excretion in Kcnj10+/+ (WT) mice and renal tubule‐specific Kcnj10−/− mice (Ks‐Kir4.1 KO).ResultsMale and female mice were continuously perfused with a no‐pressure dose of angiotensin II (200 ng/min/Kg BW) or vehicle through an osmotic pump for 24 hours. Whole‐cell recording showed that angiotensin II infusion significantly increased the Kir4.1/Kir5.1 activity and hyperpolarized DCT membrane in both male and female mice. The effect of angiotensin II on DCT membrane potential was absent in Ks‐Kir4.1 KO mice, suggesting that the stimulation of Kir4.1 was responsible for the hyperpolarization of the DCT membrane. The infusion of angiotensin II also increased the expression of pNCC and tNCC in both male and female mice. Renal clearance study has demonstrated that the thiazide‐induced renal sodium excretion was significantly larger in angiotensin II‐treated mice than those vehicle treated mice, suggesting an upregulation of NCC by angiotensin II. However, the stimulatory effect of angiotensin II on thiazide‐induced natriuresis was significantly diminished in both male and female Ks‐Kir4.1 KO mice, suggesting the role of Kir4.1 in mediating the effect of angiotensin II on NCC.ConclusionAngiotensin II stimulates the basolateral Kir4.1/Kir5.1 channel activity in the DCT. Kir4.1/Kir5.1 activity in the DCT is required for the stimulatory effect of angiotensin II on NCC activity/expression.Support or Funding InformationNational Institutes of Health grants DK54983 (to Dr. Wang)