Hypocapnia-induced contraction of porcine airway smooth muscle.
Hypocapnia constricts peripheral airways in vivo. This study investigated the role of airway smooth muscle in this phenomenon and the mechanism of hypocapnia-induced contraction in vitro. Isometric tension, intracellular pH (pHi) and intracellular free calcium concentration ([Ca2+]i) were measured in porcine airway smooth muscles suspended in organ baths in the presence of 5% or 0% CO2. In tracheal strips precontracted with carbachol, hypocapnic challenge (0% CO2) produced increases in tension, pHi, and [Ca2+]i. In bronchial rings or tracheal strips precontracted with carbachol, nifedipine administered between consecutive contractions attenuated responses to hypocapnia (75+/-11% above carbachol-precontracted tension before nifedipine versus 39+/-9% after nifedipine, n=7 bronchial rings, p<0.05). Neither indomethacin (5 microM), nordihydroguaiaretic acid (10 microM) nor phenidone (10 microM) significantly altered responses. These data suggest that enhanced Ca2+ influx through voltage-dependent Ca2+ channels of airway smooth muscle cells is important in airway responses to hypocapnia.
Lindeman
K S
KS
Dept of Anesthesiology/Critical Care Medicine, The Johns Hopkins University, Baltimore, USA.
Croxton
T L
TL
Lande
B
B
Hirshman
C A
CA
D000818:Animals; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D001993:Bronchodilator Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002245:Carbon Dioxide / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D013552:Swine; D014132:Trachea / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D001993:Bronchodilator Agents; D002121:Calcium Channel Blockers; D002245:Carbon Dioxide; D002217:Carbachol; D009543:Nifedipine; D007545:Isoproterenol; D002118:Calcium