Endothelins: functional and autoradiographic studies in guinea pig trachea.
The presence of binding sites for [125I]endothelin-1 and the contractile activities of endothelins (ETs) and sarafotoxin S6b and the endothelin fragment ET(16-21) were investigated in guinea pig trachea. ETs and sarafotoxin S6b (0.1-100 nM) induced potent contractile responses in guinea pig trachea with EC50 values ranging from 1.57 to 12.97 nM. Epithelium removal increased the potencies of ET-1, ET-2 and S6b, but not that of ET-3, and maximal responses to ET-1 and ET-2 were also increased. Effects of epithelium removal were partially mimicked by phosphoramidon (10 microM), an enkephalinase inhibitor, suggesting that enkephalinase (EC.3.4.24.11.) is able to degrade ET-1 and ET-2. ET-3-induced contractions were not affected by phosphoramidon. Autoradiographic studies suggested the presence of at least two specific binding sites for [125]ET-1 in guinea pig airway smooth muscle. The correlation between Kd and EC50 values suggests that the binding sites identified in the airway smooth muscle represent functional receptors for ETs. ET(16-21) and ET(16-21)-NH2 were less potent agonists than the ETs in guinea pig trachea and 10 microM ET(16-21) was unable to inhibit [125I]ET-1 binding in guinea pig airway smooth muscle. Therefore, these results suggest that the C-terminal hexapeptide of ET-1 cannot be used to classify ET receptors in guinea pig trachea.
Tschirhart
E J
EJ
Marion Merrell Dow Research Institute, Strasbourg, France.
Drijfhout
J W
JW
Pelton
J T
JT
Miller
R C
RC
Jones
C R
CR
D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D001345:Autoradiography; D001665:Binding Sites; D004347:Drug Interactions; D016232:Endothelins / Q000378:metabolism* / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006020:Glycopeptides / Q000494:pharmacology; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D014132:Trachea / Q000187:drug effects / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D016232:Endothelins; D006020:Glycopeptides; C008890:phosphoramidon