MULTIPLE SUBTYPES OF ENDOTHELIN RECEPTORS IN HUMAN AND PORCINE TISSUES - CHARACTERIZATION BY LIGAND-BINDING, AFFINITY LABELING, AND REGIONAL DISTRIBUTION

To characterize the properties and the distribution of endothelin (ET) receptor subtypes, we have examined the ligand selectivity and the molecular weight (M(r)) of [I-125]ET-1 and [I-125]ET-3 binding sites in various tissues of human and pigs. ET-1 and ET-2 showed almost identical potencies in displacing the bound [I-125]ET-1 in all of the tissues examined. ET-3, sarafotoxin S6b (SRTX-b), and sarafotoxin S6C (SRTX-c) displaced the [I-125]ET-1 with nearly the same sensitivity as ET-1 (IC50 = 0.07-3.0 nM) in brain, kidney, liver, and adrenal, whereas the three peptides showed very weak competition (IC50 = 40-500 nM) against [I-125]ET-1 binding in atria, aorta, lung, stomach, and uterus. The B(max) value for [I-125]ET-3 was 83% of that for [I-125]ET-1 in human liver membranes, whereas the B(max) for [I-125]ET-3 was only 12% of that for [I-125]ET-1 in human atrial membranes. [I-125]ET-3 bound to liver and atrial membranes was displaced by ET/SRTX isopeptides almost equipotently. Two proteins with M(r) of 110 and 50 kDa were specifically affinity-labeled with [I-125]ET-1 in porcine lung membranes. The above findings indicated that two distinct subclasses of ET receptors, namely ET-1/ET-2-specific and ET/SRT family common receptors, were distributed in various proportions in mammalian tissues.