[Contraction-relaxation coupling of skeletal muscle in patients susceptible to malignant hyperthermia].
OBJECTIVE
To assess whether halothane exposure could influence contraction-relaxation coupling of human skeletal muscle with malignant hyperthermia susceptibility. STUDY DESIGNED: Laboratory investigation.


METHODS
Muscle biopsies from 14 patients, including six classified as susceptible to MH (MHS) and eight as classified as non-susceptible (MHN) according to criteria of the European MH group. Mechanical parameters of strips were obtained before and after 3 vol% halothane exposure. The contraction and relaxation parameters were measured under isotonic and isometric conditions: maximum shortening and lengthening velocities (respectively maxVc and maxVr); peak of the positive (+dP/dtmax) and negative (-dP/dtmax) twitch tension derivative; ratio R1 = maxVc/maxVr and ratio R2 = (+dP/dtmax) (-dp/dtmax).


RESULTS
In MHN muscle, halothane markedly increased maxVc and maxVr, so that the ratio R1 was unchanged. Both +dP/dtmax and -dP/dtmax increased such that the ratio R2 did not vary. In MHS muscle, halothane induced a significant decrease in maxVr (p < 0.05) without changes in maxVc, so that the ratio R1 increased significantly. +dP/dtmax remained unchanged whereas -dP/dtmax decreased significantly; the ratio R2 increased (p < 0.05).


CONCLUSIONS
Our results indicated that, in MHN muscle the contractility property is improved with halothane exposure. In MHS muscle, halothane caused an impairment of relaxation. The mechanical abnormalities observed in this study might be related to sarcoplasmic reticulum dysfunction in MH diseases.
Laboratoire de pharmacologie, unité de recherche sur l'hyperthermie maligne, faculté de médecine, service CIVIS, CHRU 59045 Lille, France. sassou.etchrivi@wanadoo.fr
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Krivosic-Horber
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D006221:Halothane / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007551:Isotonic Contraction / Q000187:drug effects; D008305:Malignant Hyperthermia / Q000503:physiopathology*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*
D018685:Anesthetics, Inhalation; D006221:Halothane