In this study we characterized the endothelin (ET) receptors of cultured L6 myotubes in order to gain a further insight into the mechanism of the ET effect on skeletal muscle cells. Displacements of 125I-ET-1 by unlabeled ET-1, ET-2 and ET-3 revealed receptors with a high affinity (Kd < 1 nmol/l) to ET-1 and ET-2 and a low affinity (Kd > 100 nmol/l) to ET-3, which suggested the presence of primarily ETA receptors on L6 myotubes. These findings were complemented by displacement binding kinetics, in which the ETA receptor antagonist JKC-301 was used. More-over, the ET-1-evoked increase in the cytosolic free Ca was blocked by JKC-301 but not by the ETB receptor antagonist IRL-1038. Collectively, these findings indicate that the ET-mediated response in cultured skeletal muscle cells is through the ETA receptor.