[125I]BQ3020, a novel endothelin agonist selective for the endothelinB receptor subtype

The endothelins represent a family of three (ET-1, ET-2, and ET-3) isopeptides that are derived from vascular endothelial cells and function as potent vasoconstrictors. Two endothelin receptor subtypes, ETA and ETB, have been cloned and are structurally similar to the large family of guanine nucleotide-binding protein (G-protein) linked receptors. The ET receptor subtypes can also be distinguished by their different pharmacological profiles.. A novel linear peptide fragment of endothelin-1 (ET-1), N-acetyl-[Ala11,15]ET-1[6-21] (BQ3020) has been identified as a potent and ETB-selective agonist. [125I]BQ3020 binds with high affinity (Kd = 31 pM) and limited capacity (Bmax = 570 fmol/mg protein) to a single class of recognition sites in rat cerebellum. High affinity [125I]BQ3020 binding is reduced in the presence of guanine nucleotides indicating an interaction with high and low affinity states of the ETB receptor. This protocol describes the use of [125I]BQ3020 as a specific radioligand for the ETB receptor.