title: Gz- and not Gi-proteins are coupled to pre-junctional μ-opioid receptors in bovine airways.
abstract: We investigated the signal transmission pathway by which activation of μ-opioid receptors attenuates acetylcholine (ACh) release in bovine trachealis. Electrical stimulation (ES)-induced [(3)H]-ACh release was determined in bovine tracheal smooth muscle strips pre-incubated with either the Gi-protein inhibitor pertussis toxin (PTX, 500 ng/ml and 1 μg/ml) or the Gz-protein specific inhibitor arachidonic acid (AA, 10(-6)M and 10(-5)M) and then treated with DAMGO (D-Ala(2),N-MePhe(4),Gly-ol(5)-enkephalin) 10(-5)M. Indomethacin 10(-5)M was used to block AA cascade. The inhibitory effect of DAMGO on ES-induced [(3)H]-ACh release was PTX-insensitive, but, by contrast, ablated by AA in a concentration-dependent manner. AA 10(-5)M alone reduced [(3)H]-ACh release, an effect that was prevented by iberiotoxin 10(-7)M, suggesting an involvement of Ca(2+)-activated K(+)-channels. Western blot analysis consistently showed immunoreactive bands against a specific antibody anti-Gz-α subunit at ∼40 kDa, consistent with the presence of Gz-protein. The present findings suggest that in isolated bovine trachealis, activation of μ-opioid receptors inhibits ACh-release through a signal transmission pathway involving Gz-protein rather than Gi-protein.
authors.affiliation: Dipartimento di Medicina Interna e Specialità Mediche, University of Genoa, 16132 Genoa, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Baroffio
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Brichetto
authors.forename: Luisa
authors.initials: L
authors.lastname: Franco
authors.forename: Emanuele
authors.initials: E
authors.lastname: Crimi
authors.forename: Kai
authors.initials: K
authors.lastname: Rehder
authors.forename: Vito
authors.initials: V
authors.lastname: Brusasco
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D015153:Blotting, Western; D002417:Cattle; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014132:Trachea / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000701:Analgesics, Opioid; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016718:Arachidonic Acid; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000109:Acetylcholine
keywords: Acetylcholine; Arachidonic acid; Bovine trachealis; G proteins; Neurotransmission; Pertussis toxin