DISTINCT TISSUE DISTRIBUTION AND CELLULAR-LOCALIZATION OF 2 MESSENGER RIBONUCLEIC-ACIDS ENCODING DIFFERENT SUBTYPES OF RAT ENDOTHELIN RECEPTORS

Endothelins (ETs) are very potent vasoconstrictive peptides and have diverse functions in both vascular and nonvascular tissues. This investigation concerns the tissue distribution and cellular localization of rat mRNAs encoding two different subtypes of ET receptors (ET(A) and ET(B)). We isolated 46 cDNA clones from a rat lung cDNA library by hybridization with the bovine ET(A) cDNA. The characterization of these cDNA clones indicated that they represent either the ET(A) or ET(B) cDNA. In situ and blot hybridization analyses revealed that the rat ET(A) mRNA is predominantly expressed in vascular smooth muscle cells of a variety of tissues, bronchial smooth muscle cells, myocardium, and the pituitary gland. There is no significant expression of ET(B) mRNA in vascular smooth muscle cells, and ET(A), thus, plays a primary role in ET-induced vascular contraction. ET(B) mRNA is more widely distributed in various cell types of many tissues. Its prominent expression is seen in glial cells throughout the brain regions, epithelial cells of the choroid plexus, ependymal cells lining the ventricle, myocardium, endothelial cells of glomeruli, and epithelial cells of the thin segments of Henle's loops. Our investigation demonstrates that the mRNAs for the two subtypes of rat ET receptors show specialized expression patterns of cell types in both brain and peripheral tissues.