Natriuretic peptides and diadenosine polyphosphates modulate pH regulationof 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 intr acellular pH (pH(i)). The influence of natriuretic peptides, diadenosine po lyphosphates, 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. Th e inhibitors of Na+/H+ exchange, amiloride and HOE694, blocked pH(i) recove ry completely in the absence of and by approximately 50% in the presence of HCO3-/CO2. Natriuretic peptides (ANP, BNP, CNP, urodilatin) completely inh ibited pH(i) recovery in the absence of and by approximately 40% in the pre sence of HCO3-/CO2. These effects were abolished by the cGMP-dependent prot ein kinase inhibitor KT5823. Diadenosine polyphosphates (Ap3A-Ap6A), ATP an d 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 wa s abolished in the presence of the cAMP-dependent protein kinase inhibitor KT5720, and that of Ap5A by the protein kinase C inhibitor calphostin C. PD GF activated acid extrusion in these cells by approximately 40%. From the f our 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. T hese data suggest that in these rat mesangial cells the Na+/H+ exchanger, s pecifically the NHE-1 isoform, accounts for around 50% of pH(i) recovery fr om an acid load under physiological conditions, and that Na+/H+ exchange st imulated by acidification can be inhibited by activation of PKG, PKA, and P KC and stimulated by PDGF after acute exposition to these agonists. Copyrig ht (C) 1999 S. Karger AG, Basel.