Role of Rho GDP-dissociation inhibitor alpha in control of ENaC-mediated sodium reabsorption [Membrane Biology]

August 27th, 2014 by Pavlov, T. S., Levchenko, V., Staruschenko, A.

The epithelial sodium channel (ENaC) is expressed in the aldosterone sensitive distal nephron where it performs sodium reabsorption from the lumen. We have recently shown that ENaC activity contributes to the development of salt-induced hypertension as a result of deficiency of EGF level. Previous studies revealed that Rho GDP-dissociation inhibitor alpha (RhoGDIα) is involved in the control of salt-sensitive hypertension and renal injury via Rac1, which is a one of the small GTPases activating ENaC. Here, we investigated intracellular mechanism mediating the involvement of the RhoGDIα/Rac1 axis in the control of ENaC and effect of EGF on ENaC in this pathway. We demonstrated that RhoGDIα is highly expressed in the cortical collecting ducts of mice and rats and its expression is downregulated in Dahl SS rats fed a high salt diet. Knockdown of RhoGDIα in cultured cortical collecting duct principal cells increased ENaC subunits expression and ENaC-mediated sodium reabsorption. Furthermore, RhoGDIα deficiency causes enhanced response to EGF treatment. Patch-clamp analysis reveals that RhoGDIα significantly decreases ENaC current density and prevents its upregulation by RhoA and Rac1. Inhibition of Rho-kinase with Y27632 had no effects on ENaC response to EGF either in control or RhoGDIα knocked down cells. However, EGF treatment increased levels of active Rac1, which was further enhanced in RhoGDIα-deficient cells. We conclude that changes in RhoGDIα-dependent pathway has permissive role in the Rac1-mediated enhancement of ENaC activity observed in salt-induced hypertension.