Rat renal preglomerular vessels, glomeruli and papillae do not express detectable quantities of B-type natriuretic peptide receptor


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Abstract

DesignAtrial natriuretic factor (ANF) receptor subtypes were quantitated by radioligand studies in three different rat renal isolated tissues: preglomerular vessels, glomeruli and papillae.ResultsIn preglomerular vessels 100% of [125I]-ANF binding was displaced with high affinity by ANF. C-ANF {des-[Gln18, Ser19, Gly20, Leu21, Gly222] ANP(4–23)} a specific ligand for ANP-C receptors, displaced 30% of total binding with a lower affinity than ANF. C-type natriuretic peptide (CNP) displaced [125I]-ANF binding in a biphasic manner, indicating that it binds to two sites with affinities three orders of magnitude apart. When CNP was incubated in the presence of 0.1 $mUmol/l C-ANF to saturate ANP-C receptors, the high-affinity binding site vanished and maximum binding decreased to 70%, suggesting that CNP binds with high affinity to ANP-C receptors. Since the ANP-A receptor has little or no avidity for CNP, it is probably the low-affinity binding site. CNP and C-ANF displaced most [125I]-[Tyr]CNP(1–22) binding with very close affinities, indicating that CNP binds primarily preglomerular vascular ANP-C receptors. In glomeruli CNP behaved similarly to C-ANF in its ability to displace approximately 85% of [125I]-ANF binding; the remaining 15% was completely displaced by ANF. C-ANF and CNP inhibited 100% of [125I]-[Tyr]CNP(1–22) binding. Both findings suggest that [125I]-[Tyr]CNP(1–22) binds ANP-C receptors exclusively. In renal papillae no displacement of [125I]-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 [125I]-[Tyr]CNP(1–22) binding to papillary membranes indicates that ANP-B receptors are not expressed in that tissue. Unlike ANF, CNP stimulated cGMP production in glomeruli and papillae only at extremely high, supraphysiological concentrations.ConclusionThe present results suggest that ANP-B receptors either are absent or are present in undetectable amounts in rat renal preglomerular vessels, glomeruli and papillae.

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