Heterogeneous binding sites for alpha-atrial natriuretic peptide in human umbilical cord and placenta

The distributions of atrial natriuretic peptide (ANP) clearance receptors in human umbilical cord and placenta were investigated by using des[Gln18,Ser19,Gly20,Leu21,Gly22]ANP-(4-2 3) (C-ANP) as a specific ligand of this receptor to displace bound alpha-125I-labeled ANP. alpha-125I-ANP bound reversibly to umbilical venous and arterial intima and to fetal placental and maternal decidual tissues, with dissociation constants of 1.24 +/- 0.51, 0.58 +/- 0.19, 1.86 +/- 0.51, and 1.07 +/- 0.25 mM, respectively. Binding was reversed by 1 microM unlabeled alpha-ANP but not by unrelated peptides such as gastrin. The 1 microM C-ANP displaced bound alpha-125I-ANP from the intima of umbilical artery but not that of the vein. The specific reversible binding of alpha-125I-ANP to placental decidua but not to fetal placenta was also displaced by 1 microM C-ANP. Therefore high-affinity binding sites for alpha-ANP on the intima of the umbilical artery and on placental decidua differ from those on the umbilical vein and on fetal placental tissue; the binding sites of the intima of the umbilical artery and of the decidua in humans are consistent with clearance receptors for alpha-ANP.