The contraction-relaxation coupling of human skeletal muscle with malignant hyperthermia susceptibility.

Objective: To assess whether halothane exposure could influence contraction- relaxation coupling of human skeletal muscle with malignant hyperthermia susceptibility. Study designed. Laboratory investigation. Material and 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 3vol% 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/dt(max)) and negative (-dP/dt(max)) twitch tension derivative; ratio R1 = maxVc/ maxVr and ratio R2= (+ dP/dt(max)) (-dP/dt(max)). Results: In MHN muscle, halothane markedly increased maxVc and maxVr, so that the ratio R1 was unchanged. Both + dP/dt(max) and -dP/dt(max) 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/ dt(max) remained unchanged whereas -dP/dt(max) decreased significantly; the ratio R2 increased (p < 0.05). Conclusion: 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. (C) 2002 Editions scientifiques et medicales Elsevier SAS.