Endothelin receptors in adult human and swine isolated ventricular cardiomyocytes

The present study aimed to investigate endothelin-1 (ET-1) receptors in hum an and swine cardiomyocytes with binding studies using ETA and ETB selectiv e receptor antagonists (BMS-182874 and BQ-788, respectively). Cell distribu tion of mRNA expression for ETA and ETB subtypes was investigated by in sit u hybridization using specific cDNA probes. The I-125-ET-1 binding, which r eached equilibrium in about 120 min (K-obs = 0.051 +/- 0.003 min(-1)), was only partially displaceable by the addition of a large excess of ET-1 (abou t 15% with a half-life of 20 min). In equilibrium binding studies,I-125-ET- 1 had a K-d of 0.43 +/- 0.08 nM and a maximum binding (B-max) of 42.8 +/- 6 .6 fmol/mg protein. ETA and ETB receptors are represented in human and swin e cardiomyocytes with an 85:15 ratio as indicated by the biphasic pattern o f competition of both BMS-182874 and BQ-788. In situ hybridization studies confirmed that myocytes mainly expressed mRNA for ETA, whereas expression o f mRNA for the ETB subtype was documented in non-myocyte cells. These resul ts showed that ET-1 binds with high affinity and poor reversibility to spec ific receptors, in both human and swine isolated ventricular cardiomyocytes , without significant species differences. (C) 1999 Elsevier Science Inc.