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 EMS-182874 selectively and competitively inhibits ETA receptors both on isolated myocytes and ventricular membranes with similar to 1,300 times greater affinity for ETA than ETB subtypes. The [I-125]-ET-1 specific binding revealed 42,851 +/- 2,546 receptors/ myocyte with a prevalent proportion of ETA-receptor subtypes on both myocytes (84 +/- 2%) and ventricular membranes (66 +/- 3%). In situ hybridization studies revealed that mRNA for ETA receptors was expressed on both myocytes and nonmyocyte cells, whereas mRNA for ETB receptors was almost exclusively expressed on fibroblasts and endothelial cells. Specific binding of [I-125]-ET-1 to both myocytes and ventricular membranes in the presence of specific ETA (BMS-182874) and ETB (BQ-788)-receptor antagonists showed a displacement of [I-125]-ET-1 by unlabeled ET-1, which were significantly faster from ETB than from ETA. This suggests a clearance function of ventricular ETB receptors.