title: Different inhibitory effects of volatile anesthetics on T- and L-type voltage-dependent Ca2+ channels in porcine tracheal and bronchial smooth muscles.
abstract: BACKGROUND
  The distal airway is more important in the regulation of airflow resistance than is the proximal airway, and volatile anesthetics have a greater inhibitory effect on distal airway muscle tone. The authors investigated the different reactivities of airway smooth muscles to volatile anesthetics by measuring porcine tracheal or bronchial (third to fifth generation) smooth muscle tension and intracellular concentration of free Ca2+ ([Ca2+]i) and by measuring inward Ca2+ currents (ICa) through voltage-dependent Ca2+ channels (VDCs).
  
  
  METHODS
  Intracellular concentration of free Ca2+ was monitored by the 500-nm light emission ratio of Ca2+ indicator fura-2. Isometric tension was measured simultaneously. Whole-cell patch clamp recording techniques were used to investigate the effects of volatile anesthetics on ICa in dispersed smooth muscle cells. Isoflurane (0-1.5 minimum alveolar concentration) or sevoflurane (0-1.5 minimum alveolar concentration) was introduced into a bath solution.
  
  
  RESULTS
  The volatile anesthetics tested had greater inhibitory effects on carbachol-induced bronchial smooth muscle contraction than on tracheal smooth muscle contraction. These inhibitory effects by the anesthetics on muscle tension were parallel to the inhibitory effects on [Ca2+]i. Although tracheal smooth muscle cells had only L-type VDCs, some bronchial smooth muscle cells (approximately 30%) included T-type VDC. Each of the two anesthetics significantly inhibited the activities of both types of VDCs in a dose-dependent manner; however, the anesthetics had greater inhibitory effects on T-type VDC activity in bronchial smooth muscle.
  
  
  CONCLUSIONS
  The existence of the T-type VDC in bronchial smooth muscle and the high sensitivity of this channel to volatile anesthetics seem to be, at least in part, responsible for the different reactivities to the anesthetics in tracheal and bronchial smooth muscles.
authors.affiliation: Department of Anesthesiology, Sapporo Medical University School of Medicine, Hokkaido, Japan. yamakage@sapmed.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Yamakage
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.forename: N
authors.initials: N
authors.lastname: Tsujiguchi
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; D001980:Bronchi / Q000187:drug effects*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D020747:Calcium Channels, T-Type / Q000187:drug effects*; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D013552:Swine; D014132:Trachea / Q000187:drug effects*
chemical_list: D018685:Anesthetics, Inhalation; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D009543:Nifedipine