1 The pharmacological properties of endothelin receptors (ETR) were investigated in guinea-pig bronchus by comparing binding and functional results. 2 In binding assays, both the ETB agonists, endothelin-3 (ET-3) and N-suc-[Glu(9), Ala(11,15)]ET-1(8-21) (IRL 1620), and the antagonist, N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methyllleucyl-D-1-methoxyca rbonyltryptophanyl-D-norleucine (BQ 788), showed biphasic inhibition curves of [I-125]endothelin-1 (ET-1) binding to bronchus membranes prepared from intact or epithelium-deprived tissue. IRL 1620 did not completely displace specifically [I-125]-ET-1 bound to these tissue preparations. In the presence of the ETA-selective antagonist, cyclo(-D-Trp-D-Asp-L-Pro-D-Val-L-Leu) (BQ 123, 1 mu M), IRL 1620 displacement curves were shallow but a complete inhibition was reached at a concentration of 1 mu M. 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 mu M BQ 123. The non-selective agonist, ET-1, and BQ 123 inhibited [I-125]-ET binding to bronchus membranes in dose-dependent fashions with monophasic curves. 3 The contracting activity of IRL 1620 (0.55 nM-1.6 mu M) 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 N-omega-nitro-L-argininemethylester (L-NAME) or epithelium removal but not by pretreatment with atropine or iberiotoxin. 4 Our results demonstrate that guinea-pig bronchus contains two populations of ETB receptors with different affinities for the ETB-selective agonist, IRL 1620. One ETB receptor population appears to activate bronchial muscle contraction while another on epithelial cells causes muscle relaxation through the release of nitric oxide (NO).
Suc-[Glu9,Ala 11,15]-endothelin-1(8-21), IRL 1620, identifies two populations of ETB receptors in guinea-pig bronchus
MAZZONI, MARIA ROSA;BRESCHI, MARIA CRISTINA;GIUSTI, LAURA;NIERI, PAOLA;LUCACCHINI, ANTONIO
1999-01-01
Abstract
1 The pharmacological properties of endothelin receptors (ETR) were investigated in guinea-pig bronchus by comparing binding and functional results. 2 In binding assays, both the ETB agonists, endothelin-3 (ET-3) and N-suc-[Glu(9), Ala(11,15)]ET-1(8-21) (IRL 1620), and the antagonist, N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methyllleucyl-D-1-methoxyca rbonyltryptophanyl-D-norleucine (BQ 788), showed biphasic inhibition curves of [I-125]endothelin-1 (ET-1) binding to bronchus membranes prepared from intact or epithelium-deprived tissue. IRL 1620 did not completely displace specifically [I-125]-ET-1 bound to these tissue preparations. In the presence of the ETA-selective antagonist, cyclo(-D-Trp-D-Asp-L-Pro-D-Val-L-Leu) (BQ 123, 1 mu M), IRL 1620 displacement curves were shallow but a complete inhibition was reached at a concentration of 1 mu M. 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 mu M BQ 123. The non-selective agonist, ET-1, and BQ 123 inhibited [I-125]-ET binding to bronchus membranes in dose-dependent fashions with monophasic curves. 3 The contracting activity of IRL 1620 (0.55 nM-1.6 mu M) 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 N-omega-nitro-L-argininemethylester (L-NAME) or epithelium removal but not by pretreatment with atropine or iberiotoxin. 4 Our results demonstrate that guinea-pig bronchus contains two populations of ETB receptors with different affinities for the ETB-selective agonist, IRL 1620. One ETB receptor population appears to activate bronchial muscle contraction while another on epithelial cells causes muscle relaxation through the release of nitric oxide (NO).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
