title: Low-temperature modification of the inhibitory effects of volatile anesthetics on airway smooth muscle contraction in dogs.
abstract: BACKGROUND
  Because exposure to low temperature can modify the effect of volatile anesthetics on airway smooth muscle contraction, this study was conducted to investigate low-temperature modifications of the inhibitory effects of isoflurane and sevoflurane on canine tracheal smooth muscle tone by simultaneously measuring the muscle tension and intracellular concentration of Ca2+ ([Ca2+]i) and by measuring voltage-dependent Ca2+ channel activity.
  
  
  METHODS
  [Ca2+]i was monitored by the 500-nm light emission ratio of preloaded fura-2, a Ca2+ indicator. Isometric tension was measured simultaneously. Whole cell patch clamp recording techniques were used to observe voltage-dependent Ca2+ channel activity in dispersed muscle cells. Isoflurane (0-3.0%) or sevoflurane (0-3%) was introduced to a bath solution at various temperatures (37, 34, or 31 degrees C).
  
  
  RESULTS
  Low temperature (34 or 31 degrees C) reduced high-K+-induced (72.7 mm) muscle contraction and increased [Ca2+]i, but it enhanced carbachol-induced (1 microm) muscle contraction with a decrease in [Ca2+]i. The volatile anesthetics tested showed significant inhibition of both high-K+-induced and carbachol-induced airway smooth muscle contraction, with a concomitant decrease in [Ca2+]i. The inhibition of the carbachol-induced muscle contraction by volatile anesthetics was abolished partially by exposure to low temperature. Volatile anesthetics and low-temperature exposure significantly inhibited voltage-dependent Ca2+ channel activity of the smooth muscle.
  
  
  CONCLUSIONS
  Exposure of airway smooth muscle to low temperature leads to an increase in agonist-induced muscle contractility, with a decrease in [Ca2+]i. The inhibition of voltage-dependent Ca2+ channel activity by exposure to low temperature and by volatile anesthetics cam be attributed, at least in part, to the decrease in [Ca2+]i.
authors.affiliation: Department of Anesthesiology, Sapporo Medical University School of Medicine, Japan. yamakage@sapmed.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Yamakage
authors.forename: N
authors.initials: N
authors.lastname: Tsujiguchi
authors.forename: J
authors.initials: J
authors.lastname: Hattori
authors.forename: Y
authors.initials: Y
authors.lastname: Kamada
authors.forename: A
authors.initials: A
authors.lastname: Namiki
mesh_terms: D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D003080:Cold Temperature; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D007530:Isoflurane / Q000494:pharmacology*; D008738:Methyl Ethers / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000037:antagonists & inhibitors; D000077149:Sevoflurane; D014132:Trachea / Q000187:drug effects
chemical_list: D018685:Anesthetics, Inhalation; D015220:Calcium Channels; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane; D011188:Potassium