CHARACTERIZATION OF C-TYPE NATRIURETIC PEPTIDE RECEPTORS IN HUMAN MESANGIAL CELLS

Our aim was to examine whether the human glomerulus was a target for C-type natriuretic peptide (CNP) and how A, B and C receptors of natriuretic peptides (ANPR-A, ANPR-B, ANPR-C) were distributed in glomerular mesangial and epithelial cells. CNP stimulated cyclic GMP production in cultured human mesangial and epithelial cells with similar threshold concentrations (1 nM) and maximum effects (basal value x 30 at 1 mu M). In contrast, atrial natriuretic peptide (ANP) was only stimulatory in epithelial cells. [I-125] CNP bound specifically to mesangial cells with a K-d of 0.47 nM and B-max of 42 fmol/mg. Equilibrium of binding was obtained after four to five hours at +4 degrees C and nonspecific binding represented 10 to 20% of total binding. HS142-1 (100 mu g/ml), a specific inhibitor of ANPR-A and ANPR-B, suppressed 90% of CNP-dependent cyclic GMP production whereas it had little effect on [I-125]-CNP binding, suggesting that C receptors were largely predominant in mesangial cells. No biological effect of CNP on mesangial cells, including change in basal or angiotensin II-induced contractility and inhibition of basal or serum-dependent proliferation, could be demonstrated. Similar results were obtained with 8-bromo-cyclic GMP and sodium nitroprusside. Intraglomerular localization of ANPR-A, ANPR-B and ANPR-C mRNA was studied using reverse transcriptase-polymerase chain reaction with amplification of their corresponding cDNA by different primers. Amplification products were identified on gel electrophoresis by their predicted sizes and sequencing. ANPR-A, ANPR-B and ANPR-C mRNA were present in epithelial cells whereas only ANPR-B and ANPR-C mRNA were detected in mesangial cells. The presence of ANPR-C in both cell types was confirmed by Northern blot analysis. This study indicates that human mesangial cells, in contrast with epithelial cells, are not a target for ANP whereas both cell types respond to CNP and possess clearance receptors.