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

Abstract

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 from patients with malignant hyperthermia susceptibility. Strips were mounted horizontally at optimal length in normal Krebs–Ringer's solution and mechanical parameters were obtained before and after exposure to 3 vol.% halothane. The maximun shortening velocity at zero load ( V max) was determined by using Hill's characteristic equation. The contraction and relaxation indices were measured under isotonic and isometric conditions: maximum shortening and lengthening velocities (max V c and max V r, respectively); isometric peak twitch tension; peak of the positive (+d P/d t max) and negative (−d P/d t max) twitch tension derivative; ratio R1=max V c/max V r and ratio R2=(+d P/d t max)/(−d P/d t max). In normal muscle, halothane markedly increased V max, max V c and peak twitch tension by 30±10%, 30±5% and 40±15%, respectively. The max V r values increased concomitantly with the max V c values, such that no change in the ratio R1 was observed. Both +d P/d t max and −d P/d t max increased such that the ratio R2 did not vary. In malignant hyperthermia susceptibility muscle, halothane induced a significant decrease in V max (−30±10%) and max V r (−45±15%) without changing max V c. The decrease in max V r was greater than that of max V c, such that the ratio R1 increased significantly. Peak twitch tension and +d P/d t max remained unchanged whereas −d P/d t max decreased significantly; the ratio R2 increased by 40±10%. These results suggest that halothane alters the contractile properties of malignant hyperthermia susceptibility muscle.