title: Non-quantal release of acetylcholine in guinea-pig airways: role of choline transporter.
abstract: In the resting state, motor neurons continuously release ACh through quantal and non-quantal mechanisms, the latter through vesicular ACh transporter (VAChT) and choline transporter (ChT). Although in skeletal muscle these mechanisms have been extensively studied, the non-quantal release (NQR) from parasympathetic neurons of airway smooth muscle has not been described. Here we corroborated that the organophosphate paraoxon (acetylcholinesterase inhibitor) induced a contraction blocked by atropine (muscarinic antagonist) in guinea-pig tracheal rings. This contraction was not modified by two blockers of evoked quantal release, tetrodotoxin (voltage-dependent Na(+) channel blocker) and ω-conotoxin GVIA (N-type Ca(2+) channel blocker), nor by the nicotinic blocker hexamethonium, suggesting that acetylcholine NQR could be responsible of the paraoxon-induced contraction. We confirmed that tetrodotoxin, and to some extent -conotoxin, abolished the evoked quantal ACh release induced by electrical field stimulation. Hemicholinium-3 (ChT inhibitor), but not vesamicol (VAChT inhibitor), caused a concentration-dependent inhibition of the response to paraoxon. The highest concentration of hemicholinium-3 left ∼75% of the response to electrical field stimulation, implying that inhibition of paraoxon-induced contraction was not due to depletion of neuronal vesicles. Non-neuronal sources of ACh released through organic cation transporters were discarded because their inhibition by quinine or corticosterone did not modify the response to paraoxon. Calcium-free medium abolished the effect of paraoxon, and NiCl(2), 2-aminoethyl diphenyl-borate and SKF 96365 partly inhibited it, suggesting that non-specific cation channels were involved in the acetylcholine NQR. We concluded that a Ca(2+)-dependent NQR of ACh is present in cholinergic nerves from guinea-pig airways, and that ChT is involved in this phenomenon.
authors.affiliation: Departamento de Investigacíon en Hiperreactividad Bronquial, Instituto Nacional de Enfermedades Respiratorias, México DF, Mexico.
authors.forename: Jaime
authors.initials: J
authors.lastname: Chávez
authors.forename: Mario H
authors.initials: MH
authors.lastname: Vargas
authors.forename: José E
authors.initials: JE
authors.lastname: Cruz-Valderrama
authors.forename: Luis M
authors.initials: LM
authors.lastname: Montaño
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D027682:Cation Transport Proteins / Q000378:metabolism; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D004558:Electric Stimulation; D006168:Guinea Pigs; D006426:Hemicholinium 3 / Q000494:pharmacology; D018738:Hexamethonium / Q000494:pharmacology; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010755:Organophosphates / Q000494:pharmacology; D010261:Paraoxon / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D050494:Vesicular Acetylcholine Transport Proteins / Q000378:metabolism*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
chemical_list: D027682:Cation Transport Proteins; D002800:Cholinesterase Inhibitors; D026901:Membrane Transport Proteins; D010755:Organophosphates; D010880:Piperidines; D050494:Vesicular Acetylcholine Transport Proteins; C065637:choline transporter; D006426:Hemicholinium 3; D018738:Hexamethonium; C006189:vesamicol; D013779:Tetrodotoxin; D001285:Atropine; D020866:omega-Conotoxin GVIA; D000109:Acetylcholine; D010261:Paraoxon; D002118:Calcium