The effects of 5-HT on cholinergic contraction in human airways in vitro.
Inhaled 5-hydroxytryptamine (5-HT) causes bronchoconstriction in asthmatics, and 5-HT plasma levels are elevated in asthma. Electrical field stimulation (EFS) of human airways, in vitro, evokes cholinergic contraction mediated by the release of acetylcholine (Ach) from postganglionic cholinergic nerves. The present study investigates whether selective 5-HT agonists and antagonists can modulate EFS-induced cholinergic contraction in human airways in vitro. Human airways, obtained from resections for bronchial carcinoma or organ transplant donors, were suspended under 2-g tension, between two platinum wire electrodes, in carbogenated Krebs solution at 37 degrees C and EFS was applied (1-32 Hz, 50 V, 0.5 ms, 15 s every 4 min) to elicit cholinergic contractions. 5-HT (10 microM-0.3 mM) produced frequency- and concentration-dependent facilitation of cholinergic contraction, but did not displace the concentration/response curve to Ach. Tropisetron (1 microM), a 5-HT3 and 5-HT4 antagonist, completely blocked the facilitatory effect of 5-HT (100 microM), whereas both ondansetron (1 microM) and GR 125478D (1 microM), a selective 5-HT3 and 5-HT4 antagonist, respectively, also attenuated the 5-HT-induced enhancement of cholinergic contraction. This facilitatory effect of 5-HT was partially mimicked by both selective 5-HT3 (2-methyl-5-HT) and 5-HT4 (RS 67333 and 5-methoxytryptamine) agonists. Fluoxetine (10 microM), a 5-HT uptake inhibitor, had no effect on the 5-HT (10-100 microm) induced potentiation of cholinergic contraction. These findings suggest that 5-HT facilitates cholinergic contraction in human airways in vitro through stimulation of both prejunctional 5-HT3 and 5-HT4 receptors. This may implicate a role of 5-HT in asthma.
Dupont
L J
LJ
Pulmonary Pharmacology Unit, Laboratory of Pneumology, University Hospital Gasthuisberg, Katholieke Universiteit Leuven, Belgium.
Pype
J L
JL
Demedts
M G
MG
De Leyn
P
P
Deneffe
G
G
Verleden
G M
GM
D000109:Acetylcholine / Q000494:pharmacology; D000368:Aged; D001341:Autonomic Nervous System / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007537:Isometric Contraction / Q000187:drug effects*; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology; D012143:Respiratory Physiological Phenomena; D012137:Respiratory System / Q000187:drug effects / Q000294:innervation*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D000077526:Tropisetron
D000109:Acetylcholine; D007211:Indoles; D012701:Serotonin; D012702:Serotonin Antagonists; D017367:Selective Serotonin Reuptake Inhibitors; D000077526:Tropisetron