Distribution of endothelin receptors in saphenous veins of African Americans: Implications of racial differences

The relative density of endothelin-receptor subtypes A and B (ETA and ETB, respectively) on endothelial and smooth muscle cells is the major determina nt of the contractile response to endothelin-1 (ET-1). To investigate the e ffects of race on the distribution of ET receptors, the endothelin-receptor subtypes on membrane fractions prepared from saphenous veins obtained from African-American patients undergoing coronary bypass surgery were analyzed . Similar studies were repeated with endothelium-denuded samples to study t he role of endothelium- and smooth muscle-derived ETB receptors. Competitiv e-binding experiments on membrane fractions by using [I-125]-ET-1 and unlab eled ligands, ET-1, ET-3, sarafotoxin-6-c, and BQ-123 yielded two classes o f binding sites on endothelium-intact vessels from both female and male sub jects. In women, the maximal binding capacities were 91 +/- 6 and 67 +/- 13 fmol/mg protein for ETA and ETB receptors, respectively; the corresponding values in men were 178 +/- 19 and 127 +/- 13 fmol/mg protein. Similar expe riments performed with endothelium-denuded saphenous veins indicated the pr esence of both receptor subtypes on vascular smooth muscle, in contrast to our earlier report on the presence of only ETA receptors on vessels obtaine d from white Americans. Our findings demonstrate that the ratio and the den sity of ET receptors are different in black and white Americans.