Abstract 107: Role of Nox4 in the Control of ENaC Activity in Dahl SS Rats During the Development of Salt-induced Hypertension and Diabetic Nephropathy

Abstract

Dahl salt sensitive (SS) rat is a well-established model for studying salt-induced hypertension and associated kidney injury. We and others have previously shown that salt-sensitive hypertension is accompanied by increased renal production of reactive oxygen species (ROS) and excessive activity of ENaC in the distal nephron. To investigate role of ROS, and specifically NADPH oxidase 4 (Nox4), a primary source of ROS in the kidney, involved in the regulation of ENaC activity during the development of SS hypertension and type 1 diabetes, we performed patch clamp analysis in the cortical collecting ducts of Dahl SS rats and SS rats lacking Nox4 (Nox4 -/- ). We found that SS rats fed a 4% NaCl diet have significantly elevated ENaC activity even 3 days post diet change. ENaC activity (NP o ) was 0.57±0.08, 1.32±0.3 and 1.69±0.06 before, 3 days and 3 weeks after high salt diet, respectively. In contrast, ENaC activity was not significantly different in SS Nox4-/- animals after high salt diet. To study the role of Nox4 in hyperglycemic conditions, diabetes was induced in 6 weeks old male wild type or Nox4 -/- rats with a single i.p. injection of STZ. We found that ENaC activity in the animals that were hyperglycemic for 11 weeks was elevated compared to control rats (0.71±0.10 and 1.27±0.2; p<0.05) and this effect was mediated via changes in channel open probability. Nox4 deficiency blunts the effect of hyperglycemia on ENaC activity (in STZ-treated animals open probability significantly increased from 0.43±0.06 to 0.86±0.07 in WT rats, but in the Nox4 -/- group did not change: P o was 0.51±0.06 and 0.51±0.07, respectively) that delineates the importance of Nox4-mediated ROS production for regulation of ENaC open probability. Taken together, our data indicate that ENaC activity in Dahl SS rats is elevated following a change of salt diet (3 days and 3 weeks at high salt) and after the development of type 1 diabetes. Furthermore, Nox4 plays a crucial role in these effects of high salt and hyperglycemia on ENaC activity.