Platelet receptors for atrial natriuretic peptide in man

The aim of our study was to characterize the receptor binding of human alpha-atrial natriuretic peptide (ANP) to human blood cells. Whereas no receptors were detected on red cells, on mononuclear cells and on granulocytes, we found ANP-receptors on human platelets. The binding studies were performed by incubating 40 X 10(6) platelets with 125I-ANP and with the competing ligand, when used, in a total incubation volume of 1 ml. Centrifugation was used to separate bound from free hormone. Specific binding of 125I-ANP was rapid, saturable and reversible. A steady state was achieved within 90 minutes. Scatchard analysis of saturation and competition experiments demonstrated the existence of one class of high affinity binding sites for ANP with a Kd of 8-16pM and 10-26 receptors per cell. The Kd obtained in our binding studies was in the range of physiological ANP concentrations in human plasma (8-20pM). Although characterization of platelet ANP receptors has the inherent disadvantage that there are only few of them, they could be a useful model to investigate the ANP receptor-status under different physiological and pathological conditions in man.