title: Halothane induces calcium release from human skinned masseter muscle fibers.
abstract: BACKGROUND
  An increase in masseter muscle tone in response to halothane or succinylcholine anesthesia (or both) can be observed in healthy persons. Thus the authors compared the fiber-type halothane and succinylcholine sensitivities in human masseter and vastus lateralis muscles.
  
  
  METHODS
  Masseter and vastus lateralis muscle segments were obtained from 13 and 9 healthy persons, respectively. After chemical skinning of a single fiber and loading the sarcoplasmic reticulum with Ca++ 0.16 microM solution, halothane (0.5-4 vol% bubbled in the incubating solution), succinylcholine (0.1 microM to 10 mM), or both sensitivities were defined as the concentration inducing more than 10% of the maximum tension obtained by application of 16 microM Ca++ solution. The myofilament response to Ca++ was studied with and without halothane by observing the isometric tension of skinned masseter fibers challenged with increasing concentrations of Ca++. Muscle fiber type was determined by the difference in strontium-induced tension measurements.
  
  
  RESULTS
  A significant difference in halothane sensitivity was found between type 1 masseter fibers (0.6+/-0.2 vol%; mean +/- SD) versus type 1 (2.7+/-0.6 vol%) and type 2 vastus lateralis muscle (2.5+/-0.4 vol%). Succinylcholine did not induce Ca++ release by the sarcoplasmic reticulum. In the masseter muscle, 0.75 vol% halothane decreased the maximal activated tension by 40% but did not change the Ca++ concentration that yields 50% of the maximal tension.
  
  
  CONCLUSIONS
  The very low halothane threshold for Ca++ release from the masseter muscle usually could be counteracted by a direct negative inotropic effect on contractile proteins. However, halothane may increase the sensitivity of the sarcoplasmic reticulum Ca++ release to succinylcholine-induced depolarization, leading to an increase in masseter muscle tone.
authors: Laboratoire d'Anesthésie et de Médecine d'Urgence, Faculté de Médecine, Lille, France.
authors: H
authors: H
authors: Reyford
authors: P J
authors: PJ
authors: Adnet
authors: B
authors: B
authors: Tavernier
authors: S
authors: S
authors: Beague
authors: J
authors: J
authors: Ferri
authors: R M
authors: RM
authors: Krivosic-Horber
authors: G
authors: G
authors: Haudecoeur
mesh_terms: D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D005260:Female; D006221:Halothane / Q000494:pharmacology*; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000187:drug effects* / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism; D013390:Succinylcholine / Q000494:pharmacology
chemical_list: D018685:Anesthetics, Inhalation; D013390:Succinylcholine; D002118:Calcium; D006221:Halothane