Regional distribution of endothelin receptor in porcine cardiovascular tissues

To clarify effecting sites of endothelin (ET) in a circulation system, we have identified specific receptors for porcine ET(ET-1) and investigated the distribution in the porcine cardiovascular tissues. Scatchard analysis of 125I-porcine ET binding indicated the presence of a single class of high-affinity binding sites. The binding was highly specific for ET-1, because (1) none of the other various peptides or Ca2+-channel antagonists affected the binding, (2) the scission of disulfide bonds, the digestion of the C-terminal 6-amino acid residues, or nitrophenylsulfenylization of the C-terminal Trp21 of ET-1 markedly reduced the binding ability and, (3) ET-1 showed the highest affinity for the vascular receptor among three ET isopeptides. Cardiac atria possessed the highest density (2.7 pmol/mg protein) of ET receptors of all the tissues examined, including thoracic aorta, cardiac atria and cardiac ventriculi, basilar, renal, coronary and pulmonary branch arteries, coronary, renal and jugular veins, and small vessels of pia mater encephali. Small vessels, renal and coronary arteries also showed relatively high density (0.8-1.4 pmol/mg protein). Various veins examined also showed considerable density (0.45-0.74 pmol/mg protein). The apparent Kd of cardiac ET receptors (0.76 nM) was significantly greater than that of the receptors of the other tissue (0.06-0.14 nM). The extensive distribution and the local enrichment of ET receptor in a cardiovascular system strongly suggests that ET is one of the essential endogenous substances to control the tone of the vasculature.