Natriuretic peptides and diadenosine polyphosphates modulate pH regulation of rat mesangial cells

Modulation of cell proliferation has often been thought to be connected to changes in the activity of pH-regulatory transporters and consequently intracellular pH (pH(i)). The influence of natriuretic peptides, diadenosine polyphosphates, adenosine and ATP as well as platelet-derived growth factor (PDGF) on pH(i) regulation of cultured rat mesangial cells was examined with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The inhibitors of Na+/H+ exchange, amiloride and HOE694, blocked pH(i) recovery completely in the absence of and by approximately 50% in the presence of HCO3-/CO2. Natriuretic peptides (ANP, BNP, CNP, urodilatin) completely inhibited pH(i) recovery in the absence of and by approximately 40% in the presence of HCO3-/CO2. These effects were abolished by the cGMP-dependent protein kinase inhibitor KT5823. Diadenosine polyphosphates (Ap3A-Ap6A), ATP and adenosine also inhibited pH(i) recovery completely in the absence of and partially (30-40%) in the presence of HCO3-/CO2. The effect of adenosine was abolished in the presence of the cAMP-dependent protein kinase inhibitor KT5720, and that of Ap5A by the protein kinase C inhibitor calphostin C. PDGF activated acid extrusion in these cells by approximately 40%. From the four cloned isoforms of the Na+/H+ exchanger in the rat, only transcripts of NHE-1 were found in these mesangial cell cultures using RT-PCR analysis. These data suggest that in these rat mesangial cells the Na+/H+ exchanger, specifically the NHE-1 isoform, accounts for around 50% of pH(i) recovery from an acid load under physiological conditions, and that Na+/H+ exchange stimulated by acidification can be inhibited by activation of PKG, PKA, and PKC and stimulated by PDGF after acute exposition to these agonists. Copyright (C) 1999 S. Karger AG, Basel.