Effect of ozone exposure in vivo on response of bronchial rings in vitro: role of intracellular Ca2+.
In this study we investigated the role of intracellular Ca2+ in ozone- (O3) induced airway hyperresponsiveness. Acetylcholine-induced airway responses were measured before and after inhalation of O3 (3 ppm, 30 min) or dry air. In vitro experiments were performed with intact ring segments of third- to fifth-order bronchi. Bronchial responses to carbachol (CCh) were evaluated in Krebs solution (2.5 mM Ca2+) and in Ca(2+)-free [0.1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)] Krebs solution with or without indomethacin (IDM, 10(-5) M) and were expressed as percentage of the maximal KCl response (60 mM). Inhalation of O3, but not dry air, caused airway hyperresponsiveness to acetylcholine in vivo. Responses to 50% effective concentrations of CCh were similar in bronchial preparations from O3 and control animals (with or without IDM) in normal Krebs solution. In Ca(2+)-free solution, CCh induced a sustained (20-min) bronchial contraction. These contractions relaxed immediately when nifedipine or a high EGTA concentration was added to the organ bath. The sustained contraction was abolished when the tissues had been incubated with cyclopiazonic acid (10(-5) M), a novel inhibitor of the sarcoplasmic reticulum Ca2+ pump. After O3 exposure, responses of the bronchial smooth muscle (in Ca(2+)-free medium without IDM) were increased (P < 0.05) compared with controls during the first and second CCh stimulations. This O3-induced increase in response to CCh in Ca(2+)-free solution was abolished when the tissues were incubated with IDM.(ABSTRACT TRUNCATED AT 250 WORDS)
Montaño
L M
LM
Department of Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
Jones
G L
GL
O'Byrne
P M
PM
Daniel
E E
EE
D000818:Animals; D001980:Bronchi / Q000187:drug effects*; D016084:Bronchoconstriction / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D003470:Culture Media; D004285:Dogs; D005110:Extracellular Space / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D010126:Ozone / Q000494:pharmacology*
D003470:Culture Media; D007211:Indoles; D010126:Ozone; D002217:Carbachol; D002118:Calcium; C000543:cyclopiazonic acid; D007213:Indomethacin