The inhibitory effect of the glucagon‐like peptide‐1 analog exendin‐4 on NHE3 activity in proximal tubule cells is mediated by both PKA and EPAC signaling pathways

Abstract

Recent studies suggest a potential role for glucagon like peptide‐1 (GLP‐1) in salt and water homeostasis. Unpublished data from our laboratory indicate that exendin‐4, a GLP‐1 analog, reduces NHE3‐mediated Na/H exchange in the LLC‐PK1 cell line derived from kidney proximal tubule. The aim of this work was to define the signaling mechanisms involved in modulation of NHE3 by exendin‐4. Combination of 8‐Br‐cAMP and exendin‐4 does not result in an additive effect on the Na‐dependent intracellular pH recovery in LLC‐PK1 cells. The PKA antagonist H89 partially prevents inhibition of NHE3 activity by exendin‐4. No synergistic effect on the reduction of NHE3 activity is observed when LLC‐PK1 cells are treated simultaneously with exendin‐4 and cAMP analogs which selectively activate PKA or the exchange protein directly activated by cAMP (EPAC). Both exendin‐4 and PKA activation increase NHE3 phosphorylation levels by 70%, and this effect is completely abolished by pretreatment with H89. In contrast, EPAC activation does not alter NHE3 phosphorylation status. Collectively, these results suggest that exendin‐4 inhibition of NHE3 activity in LLC‐PK1 cells occurs through both PKA and EPAC‐dependent mechanisms.