Malignant hyperthermia: a disease of specific myofiber type?

The present study attempts to determine if malignant hyperthermia susceptibility (MHS) is limited to muscles composed predominantly of a single major fiber type. The MHS trapezius muscle (49 per cent type 1 and 51 per cent type 2 fibers) has greater abnormal contracture response to halothane or to caffeine than does MHS gracilis (11 per cent type 1 and 80 per cent type 2 fibers). The dynamic properties (contraction and relaxation times) of MHS trapezius and MHS gracilis are similar, suggesting that the greater contracture response of MHS trapezius to halothane or to caffeine is more biochemical than physiological in origin. The results of this study are discussed in relevance to the diagnosis and to aetiologic investigation of malignant hyperthermia.