Occurrence of binding sites for [125I] ANP in the myocardium but not in Purkinje fibers of the bovine heart

Atrial natriuretic peptide has frequently been detected in the cardiac conduction system and has been shown to regulate some intracellular effects in Purkinje fibers. To determine if atrial natriuretic peptide works as an autocrine and/or paracrine hormone on cardiac Purkinje fibers, we examined the different parts of the conduction system in the bovine heart by use of in vitro receptor autoradiography. In no parts of the bovine conduction system were specific binding sites for [125I] atrial natriuretic peptide observed, whereas the ventricular myocardium exhibited a large number of [125I] atrial natriuretic peptide binding sites. This is the first morphologic study showing the presence of [125I] atrial natriuretic peptide binding sites in the ventricular myocardium and their absence in the conduction system. The present observations together with results obtained in studies using other methods strongly suggest that natriuretic peptide receptors are localized on ventricular myocytes.