title: Endothelin-1 (ET-1)-induced contraction in rat isolated trachea: involvement of ETA and ETB receptors and multiple signal transduction systems.
abstract: 1. Quantitative autoradiographic, biochemical and functional studies were performed to investigate the endothelin receptor subtypes and signal transduction systems that mediate endothelin-1 (ET-1)-induced contraction in rat isolated tracheal smooth muscle. 2. Specific binding of 0.5 nM [125I]-ET-1 to tracheal smooth muscle was inhibited by at least 40% in the presence of either the ETA receptor selective ligand BQ-123 (1 microM) or the ETB receptor-selective ligand sarafotoxin S6c (30 nM), indicating the presence of both ETA and ETB receptors in this tissue. 3. ET-1 and sarafotoxin S6c were both potent spasmogens of rat isolated tracheal smooth muscle preparations. Sarafotoxin S6c-induced contractions were unaffected in the presence of the ETA receptor antagonist BQ-123 (10 microM), but were markedly attenuated in tissue previously exposed to 100 nM sarafotoxin S6c to induce ETB receptor desensitization. ET-1-induced contractions were, at most, only partially attenuated either by blocking the ETA receptor-effector system (with 10 microM BQ-123) or by desensitizing the ETB receptor-effector system with sarafotoxin S6c. However, ET-1-induced contractions were markedly attenuated by blocking both receptor-effector systems simultaneously. These findings suggest that ET-1 could induce contraction by stimulating either ETA or ETB receptors. 4. ET-1 (10 microM) induced a 7 fold increase in intracellular [3H]-inositol phosphate accumulation over basal levels in rat isolated tracheal smooth muscle. In contrast, sarafotoxin S6c (2.5 microM) increased intracellular [3H]-inositol phosphate accumulation by only 2 fold. ET-1-induced accumulation of [3H]-inositol phosphates was abolished by 10 microM BQ-123. 5. In Ca2+-free Krebs bicarbonate solution, 100 nM ET-1 induced a significantly larger contraction than that induced by 100 nM sarafotoxin S6c (46.6 +/- 5.6% C,., versus 8.8 +/- 2.8% Cmax, n = 5-7). This presumed intracellular Ca2+-dependent phase of contraction induced by ET-1 was significantly inhibited by 10 microM BQ-123 (7.5 +/- 1.0% C.). Subsequent addition of 2.5 mM Ca2+ induced a second phase of contraction. The extracellular Ca2+-dependent phase of contraction induced by ET-1 was similar inmagnitude to that induced by sarafotoxin S6c (63.6 +/- 4.5% C.. versus 58.0 +/- 3.7% C.) and was not inhibited by BQ-123. Sarafotoxin S6c-induced contractions were not inhibited by the L-type Ca2+-channel antagonists, nicardipine or verapamil.6. In summary, ETA and ETB receptors coexist in rat isolated tracheal smooth muscle and stimulation of both receptor subtypes contributes to ET-l-induced contraction in this tissue. However, stimulation of these receptor subtypes appears to induce contraction by activating different second messenger pathways; ETA receptor stimulation induces phosphoinositide turnover and subsequent release of intracellular Ca2+ whereas stimulation of ETB receptors facilitates the influx of extracellular Ca2+.
authors.affiliation: Department of Pharmacology, University of Western Australia, Nedlands.
authors.forename: P J
authors.initials: PJ
authors.lastname: Henry
mesh_terms: D000818:Animals; D001345:Autoradiography; D002217:Carbachol / Q000494:pharmacology; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000494:pharmacology*; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000096:biosynthesis; D007457:Iodine Radioisotopes; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010456:Peptides, Cyclic / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017466:Receptors, Endothelin / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014132:Trachea / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014757:Viper Venoms / Q000494:pharmacology
chemical_list: D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D007295:Inositol Phosphates; D007457:Iodine Radioisotopes; D010456:Peptides, Cyclic; D017466:Receptors, Endothelin; D014662:Vasoconstrictor Agents; D014757:Viper Venoms; C057354:sarafotoxins s6; D011189:Potassium Chloride; D002217:Carbachol; C072247:cyclo(Trp-Asp-Pro-Val-Leu)