Shortening velocity of skeletal muscle from humans with malignant hyperthermia susceptibility: effects of halothane

The aim of this investigation was to assess the effect of halothane on the velocity of shortening and lengthening of muscle from normal subjects and f rom patients with malignant hyperthermia susceptibility. Strips were mounte d horizontally at optimal length in normal Krebs-Ringer's solution and mech anical parameters were obtained before and after exposure to 3 vol.% haloth ane. The maximum shortening velocity at zero load (V-max) was determined by using Hill's characteristic equation. The contraction and relaxation indic es were measured under isotonic and isometric conditions: maximum shortenin g and lengthening velocities (maxV(c) and maxV(r), respectively); isometric peak twitch tension; peak of the positive (+dP/dt(max)) and negative (-dP/ dt(max)) twitch tension derivative; ratio R1 = maxV(c)/maxV(r) and ratio R2 = (+dP/dt(max))/(-dP/dt(max)). In normal muscle, halothane markedly increa sed V-max, maxV(c) and peak twitch tension by 30 +/- 10%, 30 +/- 5% and 40 +/- 15%, respectively. The maxV(r) values increased concomitantly with the maxV(c) values, such that no change in the ratio R1 was observed. Both +dP/ dt(max) and -dP/dt(max) increased such that the ratio R2 did not vary. In m alignant hyperthermia susceptibility muscle, halothane induced a significan t decrease in V-max (-30+/-10%) and maxV(r) (-45 +/- 15%) without changing maxV(c). The decrease in maxV(r) was greater than that of maxV(c), such tha t the ratio R1 increased significantly. Peak twitch tension and +dP/dt(max) remained unchanged whereas -dP/dt(max) decreased significantly; the ratio R2 increased by 40 +/- 10%. These results suggest that halothane alters the contractile properties of malignant hyperthermia susceptibility muscle. (C ) 2000 Elsevier Science B.V. All rights reserved.