Suc-[Glu9,Ala11,15]-endothelin-1 (8-21), IRL 1620, identifies two populations of ET(B) receptors in guinea-pig bronchus

• Published in: British journal of pharmacology 1999-07, Vol.127 (6), p.1406
• Main Authors: Mazzoni, M R, Breschi, M C, Ceccarelli, F, Lazzeri, N, Giusti, L, Nieri, P, Lucacchini, A
• Format: Article
• Language: English
• Subjects: Animals; Binding, Competitive - drug effects; Bronchi - drug effects; Bronchi - metabolism; Bronchi - physiology; Dose-Response Relationship, Drug; Endothelin-1 - metabolism; Endothelin-1 - pharmacology; Endothelins - metabolism; Endothelins - pharmacology; Enzyme Inhibitors - pharmacology; Guinea Pigs; In Vitro Techniques; Iodine Radioisotopes; Male; Muscle Contraction - drug effects; NG-Nitroarginine Methyl Ester - pharmacology; Oligopeptides - pharmacology; Peptide Fragments - metabolism; Peptide Fragments - pharmacology; Peptides, Cyclic - pharmacology; Piperidines - pharmacology; Radioligand Assay; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin - drug effects; Receptors, Endothelin - metabolism
• ISSN: 0007-1188
• DOI: 10.1038/sj.bjp.0702672

The pharmacological properties of endothelin receptors (ETR) were investigated in guinea-pig bronchus by comparing binding and functional results. In binding assays, both the ET(B) agonists, endothelin-3 (ET-3) and N-suc-[Glu9,Ala11,15]ET-1(8-21) (IRL 1620), and the antagonist, N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D- 1-methoxycarbonyltryptophanyl-D-norleucine (BQ 788), showed biphasic inhibition curves of [125I]-endothelin-1 (ET-1) binding to bronchus membranes prepared from intact or epithelium-deprived tissue. IRL 1620 did not completely displace specifically [125I]-ET-1 bound to these tissue preparations. In the presence of the ET(A)-selective antagonist, cyclo(-D-Trp-D-Asp-L-Pro-D-Val-L-Leu) (BQ 123, 1 microM), IRL 1620 displacement curves were shallow but a complete inhibition was reached at a concentration of 1 microM. Both curves were better represented by two-site models. In addition, BQ 788 competition curves became monophasic when binding experiments were performed in the presence of 1 microM BQ 123. The non-selective agonist, ET-1, and BQ 123 inhibited [125I]-ET binding to bronchus membranes in dose-dependent fashions with monophasic curves. The contracting activity of IRL 1620 (0.55 nM- 1.6 microM) was tested on multiple-ring bronchial preparations pretreated with peptidase and cyclo-oxygenase inhibitors. BQ 788 shifted IRL1620 concentration-response curves to the right while BQ 123 did not influence bronchial responsiveness. In addition, a potentiation of the maximal response to the agonist was observed in BQ 788 treated bronchial rings. This effect was abolished by tissue pretreatment with Nomega-nitro-L-argininemethylester (L-NAME) or epithelium removal but not by pretreatment with atropine or iberiotoxin. Our results demonstrate that guinea-pig bronchus contains two populations of ET(B) receptors with different affinities for the ET(B)-selective agonist, IRL 1620. One ET(B) receptor population appears to activate bronchial muscle contraction while another on epithelial cells causes muscle relaxation through the release of nitric oxide (NO).