RAT RENAL PREGLOMERULAR VESSELS, GLOMERULI AND PAPILLAE DO NOT EXPRESS DETECTABLE QUANTITIES OF B-TYPE NATRIURETIC PEPTIDE RECEPTOR

Design: Atrial natriuretic factor (ANF) receptor subtypes were quantit ated by radioligand studies in three different rat renal isolated tiss ues: preglomerular vessels, glomeruli and papillae. Results: In preglo merular vessels 100% of [I-125]-ANF binding was displaced with high af finity by ANF. C-ANF Gln(18),Ser(19),Gly(20),Leu(21),Gly(22)]ANP(4-23) } a specific ligand for ANP-C receptors, displaced 30% of total bindin g with a lower affinity than ANF. C-type natriuretic peptide (CNP) dis placed [I-125]-ANF binding in a biphasic manner, indicating that it bi nds to two sites with affinities three orders of magnitude apart. When CNP was incubated in the presence of 0.1 mu mol/l C-ANF to saturate A NP-C receptors, the high-affinity binding site vanished and maximum bi nding decreased to 70%, suggesting that CNP binds with high affinity t o ANP-C receptors. Since the ANP-A receptor has little or no avidity f or CNP, it is probably the low-affinity binding site. CNP and C-ANF di splaced most [I-125]-[Tyr]CNP(1-22) binding with very close affinities , indicating that CNP binds primarily preglomerular vascular ANP-C rec eptors. In glomeruli CNP behaved similarly to C-ANF in its ability to displace approximately 85% of [I-125]-ANF binding; the remaining 15% w as completely displaced by ANF. C-ANF and CNP inhibited 100% of [I-125 ]-[Tyr]CNP(1-22) binding. Both findings suggest that [I-125]-[Tyr]CNP( 1-22) binds ANP-C receptors exclusively. In renal papillae no displace ment of [I-125]-ANF by C-ANF was observed, and CNP was bound to ANP-A receptors with the same very low affinity as in preglomerular vessels. The absence of [I-125]-[Tyr]CNP(1-22) binding to papillary membranes indicates that ANP-B receptors are not expressed in that tissue. Unlik e ANF, CNP stimulated cGMP production in glomeruli and papillae only a t extremely high, supraphysiological concentrations. Conclusion: The p resent results suggest that ANP-B receptors either are absent or are p resent in undetectable amounts in rat renal preglomerular vessels, glo meruli and papillae.