Molecular cloning of two subtypes of human endothelin receptor

We isolated complementary DNA (cDNA) clones encoding two subtypes of human endothelin receptor (ETR), ET(A)R and ET(B)R. The cDNA for ET(A)R encoded a 427-amino-acid protein. The rank order of the binding affinity to ET(A)R expressed in COS-7 cells was ET-1 ≥ ET-2 >> ET-3. The clones for human ET(B)R, different in the length of their 3'-untranslated regions, encoded the same 442-amino-acid protein. The rank order of the binding affinity of ET isopeptides (ET-1, ET-2, and ET-3) to ET(B)R expressed in COS-7 cells was ET-1 = ET-2 = ET-3. Both ET(A)R and ET(B)R had a transmembrane topology similar to that of other G-protein-coupled receptors. Northern blot analysis of ET(A)R revealed a single band with a size of 4.3 kb in a wide variety of human tissues, especially in the blood vessel. Northern blot analysis of ET(B)R identified three mRNA species, 4.3, 2.7, and 1.7 kb in size. These mRNAs were also expressed in a wide variety of human tissues, at the highest level in the brain and at a significant level in cultured endothelial cells.