[3H]BQ-123, a highly specific and reversible radioligand for the endothelin ETA receptor subtype

• Published in: European journal of pharmacology 1995-02, Vol.274 (1-3), p.1-6
• Main Authors: IHARA, M, YAMANAKA, R, OHWAKI, K, OZAKI, S, FUKAMI, T, ISHIKAWA, K, TOWERS, P, YANO, M
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Azepines - metabolism; Binding, Competitive; Biological and medical sciences; Cell receptors; Cell structures and functions; Endothelin Receptor Antagonists; Endothelins - antagonists & inhibitors; Endothelins - metabolism; Fundamental and applied biological sciences. Psychology; Humans; Indoles - metabolism; Isotope Labeling; Molecular and cellular biology; Molecular Sequence Data; Neuroblastoma - metabolism; Neuroblastoma - pathology; Neuropeptide receptors; Oligopeptides - metabolism; Peptides, Cyclic - metabolism; Radioligand Assay; Receptor, Endothelin A; Receptors, Endothelin - metabolism; Structure-Activity Relationship; Tritium; Tumor Cells, Cultured
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/0014-2999(94)00670-3

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.