Mazzoni M R, Breschi M C, Ceccarelli F, Lazzeri N, Giusti L, Nieri P, Lucacchini A
Department of Psychiatry, Neurobiology, Pharmacology and Biotechnology, University of Pisa, Italy.
Br J Pharmacol. 1999 Jul;127(6):1406-14. 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).
通过比较结合和功能结果，研究了豚鼠支气管中内皮素受体（ETR）的药理学特性。在结合试验中，ET（B）激动剂内皮素-3（ET-3）和N-琥珀酰-[Glu9，Ala11，15]ET-1(8 - 21)（IRL 1620）以及拮抗剂N-顺式-2,6-二甲基哌啶羰基-L-γ-甲基亮氨酰-D-1-甲氧基羰基色氨酰-D-正亮氨酸（BQ 788），均显示出[125I]-内皮素-1（ET-1）与完整或去除上皮组织制备的支气管膜结合的双相抑制曲线。IRL 1620不能完全取代特异性结合于这些组织制剂的[125I]-ET-1。在ET（A）选择性拮抗剂环（-D-色氨酸-D-天冬氨酸-L-脯氨酸-D-缬氨酸-L-亮氨酸）（BQ 123，1 microM）存在下，IRL 1620的置换曲线较平缓，但在1 microM浓度时可达到完全抑制。两条曲线用双位点模型能更好地表示。此外，当在1 microM BQ 123存在下进行结合实验时，BQ 788的竞争曲线变为单相。非选择性激动剂ET-1和BQ 123以单相曲线的剂量依赖性方式抑制[125I]-ET与支气管膜的结合。在经肽酶和环氧化酶抑制剂预处理的多环支气管制剂上测试了IRL 1620（0.55 nM - 1.6 microM）的收缩活性。BQ 788使IRL1620的浓度-反应曲线右移，而BQ 123不影响支气管反应性。此外，在BQ 788处理的支气管环中观察到对激动剂最大反应的增强。用Nω-硝基-L-精氨酸甲酯（L-NAME）预处理组织或去除上皮可消除此效应，但用阿托品或iberiotoxin预处理则不能。我们的结果表明，豚鼠支气管含有对ET（B）选择性激动剂IRL 1620具有不同亲和力的两种ET（B）受体群体。一种ET（B）受体群体似乎激活支气管肌肉收缩，而另一种在上皮细胞上通过释放一氧化氮（NO）引起肌肉松弛。
