Deficient regulation of the epithelial Na+ channel (ENaC) activity and impaired urinary conservation of Na+ in Epac1 ‐/‐ and Epac2 ‐/‐ mice

Abstract

Exchange proteins directly activated by cAMP (Epacs) are abundantly expressed in the renal tubules. We used genetic and pharmacological tools in combination with balance, electrophysiological and biochemical approaches to examine the role of Epac1 and Epac2 in renal sodium handling. We demonstrate that Epac1‐/‐ and Epac2‐/‐ mice exhibit a delayed anti‐natriuresis to dietary sodium restriction despite augmented aldosterone levels. This was associated with a significantly lower response to the epithelial Na+ channel (ENaC) blocker amiloride, reduced ENaC activity in split‐opened collecting ducts, and defective posttranslational processing of α and γENaC subunits in the knockout mice fed with Na+ deficient diet. Concomitant deletion of both isoforms led to a marginally greater natriuresis but further increased aldosterone levels. Epac2 blocker, ESI‐05 and Epac1&2 blocker, ESI‐09 decreased ENaC activity in EpacWT mice kept on Na+ deficient diet but not on the regular diet. ESI‐09 injections led to natriuresis in EpacWT mice on Na+ deficient diet, which was caused by ENaC inhibition. In summary, our results demonstrate non‐redundant actions of Epac1 and Epac2 in stimulation of ENaC activity during variations in dietary salt intake. We speculate that inhibition of Epac signaling could be instrumental in treatment of hypertensive states associated with ENaC over‐activation.