Characterization of endothelin-1 receptor subtypes in isolated human cardiomyocytes

On cardiac membranes and isolated cardiomyocytes from the human heart, cell-type distribution and functional activities of endothelin-1 (ET-1) receptor subtypes were investigated by using binding methods and messenger RNA (mRNA) in situ hybridization. The ET-receptor antagonist BMS-182874 selectively and competitively inhibits ET(A) receptors both on isolated myocytes and ventricular membranes with approximately 1,300 times greater affinity for ET(A) than ET(B) subtypes. The [125I]-ET-1 specific binding revealed 42.851+/-2,546 receptors/myocyte with a prevalent proportion of ET(A)-receptor subtypes on both myocytes (84+/-2%) and ventricular membranes (66+/-3%). In situ hybridization studies revealed that mRNA for ET(A) receptors was expressed on both myocytes and nonmyocyte cells, whereas mRNA for ET(B) receptors was almost exclusively expressed on fibroblasts and endothelial cells. Specific binding of [125I]-ET-1 to both myocytes and ventricular membranes in the presence of specific ET(A) (BMS-182874) and ET(B) (BQ-788)-receptor antagonists showed a displacement of [125I]-ET-1 by unlabeled ET-1, which were significantly faster from ET(B) than from ET(A). This suggests a clearance function of ventricular ET(B) receptors.