The Na/H-exchanger 3 (NHE3) is expressed in the brush border membrane (BBM) of proximal tubules. Its activity is downregulated upon increases in intracellular cAMP. cAMP signals through activation of PKA and/or the exchange protein directly activated by cAMP (EPAC). The aim of this work was to analyze the renal expression of EPAC1 and to investigate the role of PKA and EPAC in the regulation of NHE3 by cAMP.

EPAC1 was detected in the BBM of proximal tubules, where it colocalized with NHE3. Treatment of OK cells and murine kidney slices with cAMP analogs which selectively activate PKA or EPAC allowed us to conclude that: a) specific activation of either pathway resulted in a concentration-dependent inhibition of NHE3 activity; b) the EPAC-induced effect was independent of PKA as indicated by the lack of activation of the kinase and the insensitivity to the PKA-inhibitor H89; c) both PKA and EPAC inhibited NHE3 activity without inducing changes in the surface expression of the transporter; d) inhibition of MEK1/2 partially blocked the PKA effect whereas it fully prevented the EPAC response; e) PKA but not EPAC activation led to an increase of NHE3 phosphorylation. Thus, EPAC may represent a novel mechanism involved in the regulation of NHE3 by cAMP.