Endocardial localization and characterization of natriuretic peptide binding sites in human fetal and adult heart.

Specific, high affinity binding sites for 125I-human-alpha-atrial natriuretic peptide-(1-28)) (125I-hANP-(1-28)) were identified in human fetal and adult heart and the binding characterized using quantitative in vitro autoradiography. Binding sites were localized to atrial and ventricular endocardium, aorta, pulmonary arteries and epicardial mesothelium. Kinetic studies indicated a Kd value of 32 pM for ventricular endocardial 125I-hANP-(1-28) binding. The binding was completely inhibited by an excess (1 microM) of unlabelled hANP-(1-28), human brain natriuretic peptide-(1-32) (hBNP-(1-32)) and by the 'clearance receptor' specific ring-deleted analogue, C-ANP-(4-23). Competitive inhibition studies indicated a relative inhibitory potency for hBNP-(1-32) and C-ANP-(4-23) of 6% and 3% respectively. The data suggest that a distinct natriuretic peptide receptor subtype is expressed in the endocardium and in addition to a possible clearance function, may represent a site for feedback regulation and peptide interaction.