Regulation of Na+/H+ exchanger NHE3 by glucagon-like peptide 1 receptor agonist exendin-4 in renal proximal tubule cells

1 Department of Physiology and Biophysics, Institute of Biomedical Sciences; ; 2 Heart Institute (InCor), Medical School, University of São Paulo, and ; 3 Department of Physiology, Federal University of São Paulo, São Paulo, Brazil Submitted February 12, 2009 ; accepted in final form September 17, 2009 The gut incretin hormone glucagon-like peptide 1 (GLP-1) is released in response to ingested nutrients and enhances insulin secretion. In addition to its insulinotropic properties, GLP-1 has been shown to have natriuretic actions paralleled by a diminished proton secretion. We therefore studied the role of the GLP-1 receptor agonist exendin-4 in modulating the activity of Na + /H + exchanger NHE3 in LLC-PK 1 cells. We found that NHE3-mediated Na + -dependent intracellular pH (pH i ) recovery decreased 50% after 30-min treatment with 1 nM exendin-4. Pharmacological inhibitors and cAMP analogs that selectively activate protein kinase A (PKA) or the exchange protein directly activated by cAMP (EPAC) demonstrated that regulation of NHE3 activity by exendin-4 requires activation of both cAMP downstream effectors. This conclusion was based on the following observations: 1 ) the PKA antagonist H-89 completely prevented the effect of the PKA activator but only partially blocked the exendin-4-induced NHE3 inhibition; 2 ) the MEK1/2 inhibitor U-0126 abolished the effect of the EPAC activator but only diminished the exendin-4-induced NHE3 inhibition; 3 ) combination of H-89 and U-0126 fully prevented the effect of exendin-4 on NHE3; 4 ) no additive effect in the inhibition of NHE3 activity was observed when exendin-4, PKA, and EPAC activators were used together. Mechanistically, the inhibitory effect of exendin-4 on pH i recovery was associated with an increase of NHE3 phosphorylation. Conversely, this inhibition took place without changes in the surface expression of the transporter. We conclude that GLP-1 receptor agonists modulate sodium homeostasis in the kidney, most likely by affecting NHE3 activity. dipeptidyl peptidase IV; sodium reabsorption; intracellular pH; protein kinase A; exchange protein directly activated by cAMP Address for reprint requests and other correspondence: A. C. C. Girardi, Institute of Heart—Laboratory of Genetics and Molecular Cardiology, Univ. of São Paulo Medical School, Avenida Dr. Enéas de Carvalho Aguiar, 44, 10° andar, Bloco II, 05403-900 São Paulo, SP, Brazil (e-mail: adriana.girardi{at}incor.usp.br ).