Natriuretic Peptides and Diadenosine Polyphosphates Modulate pH Regulation of Rat Mesangial Cells

Abstract

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.

Phosphodiesterase 5A Inhibition Induces Na + /H + Exchanger Blockade and Protection Against Myocardial Infarction

“…Although inhibition of cardiac NHE-1 by PKG was previously unknown, PKG-mediated NHE-1 inhibition has been already described in mesangial cells 12 and in ocular nonpigmented ciliary epithelium. 31 In addition, it has been reported that an increase in the cGMP-PKG pathway can decrease the activity of other NHE isoforms.…”

“…11 More interestingly, this inhibition was accompanied by beneficial effects. 11 Because an increase in protein kinase G (PKG) activity in renal mesangial cells inhibited NHE activity only after an acidic load but not in basal conditions, 12 we hypothesized that the same pattern may be reproduced in myocardial tissue by chronic inhibition of the cGMP-catabolizing enzyme phosphodiesterase 5A (PDE5A). We will provide evidence that NHE-1 inhibition, after an acidic load but not under basal conditions, can be obtained by PDE5A inhibition and that this inhibition has beneficial effects on cardiac remodeling and function after experimental MI in the rat heart.…”

Enhanced Activity of the Myocardial Na + /H + Exchanger NHE-1 Contributes to Cardiac Remodeling in Atrial Natriuretic Peptide Receptor–Deficient Mice

“…For pH i measurements, the cells were transferred to a superfusion chamber, mounted on an inverted microscope (Axiovert 135, Zeiss), and incubated with the membrane-permeable fluorescent dye BCECF-AM (2 mol/L, dissolved in 0.1 g/L Pluronic F-127 in cell culture medium). 7 Loaded cardiomyocytes were excited at 488 and 436 nm, and emitted fluorescence was detected at 520 to 560 nm. 7 The ratio of fluorescence (488/436) was calculated.…”

The mechanism of action of the antidiuretic peptide Tenmo ADFa in Malpighian tubules ofAedes aegypti

“…Cyclic GMP is reported to inhibit Na/K/2Cl transport in rabbit cardiomyocytes (Clemo and Baumgarten, 1995;Lew et al, 1997) and HeLa cells (Kort and Koch, 1990). The nucleotide is known to inhibit Na/H exchange in renal proximal tubules (Roczniak and Burns, 1996), small intestine (Fawcus et al, 1997), rat mesangial cells (Schulte et al, 1999) and in epithelial cell lines such as Caco-2 (Gill et al, 2002) and human intestinal C2/bbe (McSwine et al, 1998). Accordingly, a fourth hypothesis regarding the mechanism of action of ADF and cGMP proposes the inhibition of Na/H exchange transport and Na/K/2Cl cotransport.…”