CHARACTERIZATION OF RECEPTORS FOR THE ATRIAL-NATRIURETIC-FACTOR IN RAT RENAL MICROVESSELS

Objective: To characterize [I-125]-atrial natriuretic factor [ANF-(99- 126)] binding sites in the renal preglomerular microvasculature of Spr ague-Dawley rats. Methods: Renal preglomerular microvessels were isola ted by infusion of a magnetized iron oxide solution into the renal art eries and detachment from non-vascular tissue by a magnetic field. In order to characterize [I-125]-ANF-(99-126) binding sites, saturation a nd competitive binding experiments were performed. To evaluate the pro portions of ANF receptor subtypes (ANF-R1, ANF-R2), competition curves were charted in the presence of 10(-6) mol/l C-ANF-(4-23), a specific ligand of ANF-R2 (ANP-C). Results: [I-125]-ANF binding to vascular me mbranes was saturable and of high affinity. Equilibrium saturation bin ding curves suggested the presence of one group of high-affinity recep tors [equilibrium dissociation constant (K(d)) 22+/-6 pmol/l; binding capacity (B(max)) 118+/-6 fmol/mg protein]. In competitive inhibition experiments, no significant differences were found in binding capacity between experiments performed either in the presence or in the absenc e of an excess (1 mumol/l) of C-ANF (94 +/- 27 versus 151 +/- 35 fmol/ mg protein, respectively), suggesting that most receptors in the renal vasculature are of the subtype ANF-R1. Incubation of renal microvesse ls with ANF-(99-126) stimulated cyclic GMP production in a dose-relate d manner. In parallel studies, the proportion of ANF-R1 (ANP-A, -B) an d ANF-R2 (ANP-C) receptors in glomeruli, calculated from competitive i nhibition experiments, was 86+/-2 and 14+/-2%, respectively (P<0.005). Conclusions: These results indicate that rat renal preglomerular micr ovessels contain a high proportion of guanylate cyclase-coupled ANF-R1 (ANP-A, -B) and a low density of ANF-R2 (ANP-C) receptors. This diffe rence in the proportion of ANF receptor subtypes, compared to that rep orted,in glomeruli and other vascular beds, may have physiological sig nificance.