Molecular Characterization of a Novel Human Endothelin Receptor Splice Variant

Endothelin receptors are widely distributed throughout a number of tissues. A novel ET(B) receptor splice variant (ET(B)-SVR) was identified from a human placental cDNA library, Sequence analysis indicated that the ET(B)-SVR is 436 amino acids long and shares 91% identity to the human ET(B)-R. Northern blot analysis indicated an mRNA species of 2.7 kilobases, which is expressed in the lung, placenta, kidney, and skeletal muscle. Ligand binding studies of the cloned ET(B)-SVR and ET(B)-R receptors expressed in COS cells showed that ET peptides exhibited similar potency in displacing I-125-ET-1 binding. Functional studies showed that ET-1, ET-3, and sarafotoxin 6c displayed similar potencies for inositol phosphates accumulation in ET(B)-R-transfected COS cells, whereas no increase in inositol phosphate accumulation was observed in ET(B)-SVR-transfected cells. In addition, exposure of ET(B)-R-transfected cells to ET-1 caused an increase in the intracellular acidification rate whereas ET(B)-SVR-transfected cells did not respond to ET-1. These data suggest that the ET(B)-SVR and ET(B)-R are functionally distinct and the difference in the amino acid sequences between the two receptors may determine functional coupling. Availability of cDNA clones for endothelin receptors can facilitate our understanding of the role of ET in the pathophysiology of various diseases.