Renal receptors for atrial and C-type natriuretic peptides in the rat

Receptors for alpha-atrial natriuretic peptide (alpha-ANP) and C-type natriuretic peptide [CNP-(1-22)] were quantified in kidneys from adult Wistar rats by in vitro autoradiography. 125I-labeled alpha-ANP (100 pM) bound reversibly to glomeruli, outer medullary vasa recta, and inner medulla with an apparent dissociation constant (Kd) of 3-6 nM. The presence of 10 microM des-[Gln18,Ser19,Gly20,Leu21,Gly22]ANP-(4- 23) (C-ANP), a specific ligand of the ANPR-C subtype of alpha-ANP receptor, inhibited approximately 50% of the glomerular binding of 125I-alpha-ANP, and this moiety of glomerular binding was also inhibited by CNP-(1-22) with an apparent inhibitory constant (Ki) of 10.47 +/- 7.59 nM. C-ANP and CNP-(1-22) showed little affinity for the medullary binding sites of alpha-ANP. 125I-[Tyr0]CNP-(1-22) (110 pM) bound solely to glomeruli and was competitively displaced by increasing concentrations of [Tyr0]CNP-(1-22) with an apparent Kd of 1.42 +/- 0.48 nM. Binding of increasing concentrations (25 pM to 1 nM) of 125I-[Tyr0]CNP-(1-22) in the presence or absence of 1 microM [Tyr0]CNP-(1-22) also demonstrated a high affinity (Kd of 0.41 +/- 0.07 nM) for the glomerular binding of 125I-[Tyr0]CNP-(1-22). Bound 125I-[Tyr0]CNP-(1-22) could be displaced by excess alpha-ANP and excess CNP-(1-22), both with high affinities. The glomerular binding of 125I-[Tyr0]CNP-(1-22) was also prevented by 10 microM C-ANP. Guanosine 3',5'-cyclic monophosphate produced by isolated glomeruli was measured by radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)