Receptors for atrial natriuretic factor in cardiomyocytes and aortic smooth muscle

The aim of this work was to investigate whether specific receptors for atrial natriuretic factor (ANF) are present in ventricular cardiomyocytes and aortic smooth muscle membranes. 125I-ANF was employed to test the binding of the radioligand to isolated rat cardiomyocytes. Calcium-tolerant ventricular cardiomyocytes were obtained by retrograde perfusion with collagenase. 125I-ANF binding to cardiomyocytes was highly specific (70-80%) with a KD value of 72.6 pM and a Bmax of 9.37 fmol/mg protein. In other studies, 125I-ANF binding was investigated with a membrane preparation obtained from calf thoracic aorta, from which the endothelium had been previously stripped off. In this preparation too the interaction of 125I-ANF (70-80%) was highly specific, with a KD value of 70.4 pM and a Bmax of 8.78 fmol/mg protein. These results suggest that specific receptors to atrial natriuretic factor are present both in isolated rat cardiomyocytes and in the smooth muscle of calf thoracic aorta. This second observation is in agreement with the hypothesis that the vasodilator effect of atrial natriuretic factor is due to a direct interaction between this peptide and vascular smooth muscle cells.