Identification of endothelin receptor subtypes in rat kidney cortex using subtype-selective ligands.
125I-Endothelin (ET)-1 and 125I-ET-3 displayed specific, saturable, and high affinity binding to membranes prepared from rat kidney cortex. Saturation binding experiments using 125I-ET-1 and 125I-ET-3 revealed that 125I-ET-3 binding sites were 40-50% less abundant than 125I-ET-1 binding sites. The dissociation constants (Kd) and maximum binding (Bmax) for 125I-ET-1 and 125I-ET-3 with these membranes were 218 +/- 23 pM and 275 +/- 20 fmol/mg of protein and 207 +/- 19 pM and 113 +/- 17 fmol/mg of protein, respectively. In the presence of 10 nM sarafotoxin 6c, a selective agonist for ETb receptors, 125I-ET-1 binding was decreased by 45-50% and 125I-ET-3 binding was totally abolished, suggesting that approximately 40-50% of kidney cortex ET receptors are of the ETB subtype and that 125I-ET-1 binds to both ETA and ETB receptors with the same high affinity, whereas 125I-ET-3 binds to only ETB receptors with high affinity. In addition, in the presence of BQ123 [cyclo(D-Trp,D-Asp,L-Pro,D-Val,L-Leu)], a selective antagonist for ETA receptors, 125I-ET-1 binding was decreased by 50%, whereas 125I-ET-3 binding was unaffected. Our results strongly suggest that rat kidney cortex contains ETA and ETB receptors in a 50:50 ratio and that sarafotoxin 6c and BQ123 are valuable tools in identifying the subtypes of ET receptors in various tissues.
Nambi
P
P
Department of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406-0939.
Wu
H L
HL
Pullen
M
M
Aiyar
N
N
Bryan
H
H
Elliott
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D016232:Endothelins / Q000378:metabolism; D007457:Iodine Radioisotopes; D007672:Kidney Cortex / Q000378:metabolism / Q000648:ultrastructure*; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000145:classification* / Q000378:metabolism; D017466:Receptors, Endothelin; D014757:Viper Venoms / Q000494:pharmacology
D016232:Endothelins; D007457:Iodine Radioisotopes; D010456:Peptides, Cyclic; D011956:Receptors, Cell Surface; D017466:Receptors, Endothelin; D014757:Viper Venoms; C057354:sarafotoxins s6; C072247:cyclo(Trp-Asp-Pro-Val-Leu)