Endothelin receptors in adult human and swine isolated ventricular cardiomyocytes.

ABSTRACT. The present study aimed to investigate endothelin-1 (ET-1) receptors in human and swine cardiomyocytes with binding studies using ETA and ETB selective receptor antagonists (BMS-182874 and BQ-788, respectively). Cell distribution of mRNA expression for ETA and ETB subtypes was investigated by in situ hybridization using specific cDNA probes. The 125I-ET-1 binding, which reached equilibrium in about 120 min (Kobs 5 0.051 6 0.003 min21), was only partially displaceable by the addition of a large excess of ET-1 (about 15% with a half-life of 20 min). In equilibrium binding studies, 125I-ET-1 had a Kd of 0.43 6 0.08 nM and a maximum binding (Bmax) of 42.8 6 6.6 fmol/mg protein. ETA and ETB receptors are represented in human and swine cardiomyocytes with an 85:15 ratio as indicated by the biphasic pattern of competition of both BMS-182874 and BQ-788. In situ hybridization studies confirmed that myocytes mainly expressed mRNA for ETA, whereas expression of mRNA for the ETB subtype was documented in non-myocyte cells. These results showed that ET-1 binds with high affinity and poor reversibility to specific receptors, in both human and swine isolated ventricular cardiomyocytes, without significant species differences. BIOCHEM PHARMACOL 58;2: 369–374, 1999. © 1999 Elsevier Science Inc.