title: [3H]BQ-123, a highly specific and reversible radioligand for the endothelin ETA receptor subtype.
abstract: The mode of binding of [3H]BQ-123 (cyclo(-D-Trp-D-Asp-[prolyl-3,4 (n)-[3H]]Pro-D-Val-Leu)), an endothelin receptor antagonist radioligand, was evaluated in the human neuroblastoma cell line SK-N-MC at 37 degrees C. Scatchard analysis indicated the presence of a single class of [3H]BQ-123 binding sites with a high affinity of 3.2 nM. [3H]BQ-123 binding achieved steady state within 7 min and dissociated with a half-time of 1.4 min, while [125I] endothelin-1 binding barely reached a steady state even after 6 h and showed little dissociation. [3H]BQ-123 binding was sensitive to endothelin-1 and endothelin-2 (Ki values = 0.058 and 0.10 nM, respectively) and the endothelin ETA receptor-selective antagonist BQ-123 (Ki = 3.3 nM), while showing low affinity for endothelin-3 (Ki = 50 nM), the endothelin ETB receptor-selective agonist BQ-3020 (Ki = 970 nM) and other bioactive peptides. Thus, [3H]BQ-123 is a specific and reversible radioligand for endothelin ETA receptors. The rapid reversibility of [3H]BQ-123 binding should provide a tool for estimating the equilibrium inhibition constants (Ki values) of various compounds for endothelin ETA receptors.
authors.affiliation: Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd., Japan.
authors.forename: M
authors.initials: M
authors.lastname: Ihara
authors.forename: R
authors.initials: R
authors.lastname: Yamanaka
authors.forename: K
authors.initials: K
authors.lastname: Ohwaki
authors.forename: S
authors.initials: S
authors.lastname: Ozaki
authors.forename: T
authors.initials: T
authors.lastname: Fukami
authors.forename: K
authors.initials: K
authors.lastname: Ishikawa
authors.forename: P
authors.initials: P
authors.lastname: Towers
authors.forename: M
authors.initials: M
authors.lastname: Yano
mesh_terms: D000595:Amino Acid Sequence; D001381:Azepines / Q000378:metabolism; D001667:Binding, Competitive; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007211:Indoles / Q000378:metabolism; D007553:Isotope Labeling; D008969:Molecular Sequence Data; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology; D009842:Oligopeptides / Q000378:metabolism; D010456:Peptides, Cyclic / Q000378:metabolism*; D011869:Radioligand Assay; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000378:metabolism; D013329:Structure-Activity Relationship; D014316:Tritium; D014407:Tumor Cells, Cultured
chemical_list: D001381:Azepines; D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D007211:Indoles; D009842:Oligopeptides; D010456:Peptides, Cyclic; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D014316:Tritium; C072485:cyclo(sulfoalanyl-prolyl-valyl-leucyl-tryptophyl); C083116:BQ 485; C087220:BQ 610; C079574:FR 139317; C072247:cyclo(Trp-Asp-Pro-Val-Leu)