Effects of temperature, adenosine triphosphate and magnesium concentrations on the contraction of actomyosin isolated from halothane-sensitive and -insensitive German Landrace pigs.

The effects of temperature, adenosine triphosphate and magnesium on the calcium sensitivity of actomyosin were investigated on actomyosin obtained from six halothane-sensitive and five halothane-resistant German Landrace pigs. No difference in the contractile properties was found in actomyosin from the two types of pig. However, in both types calcium sensitivity of the actomyosin was lost at temperatures slightly greater than those occurring physiologically. Both ATP and Mg2+ protect against the loss of calcium sensitivity. These results suggest that the basic lesion in halothane-induced malignant hyperthermia does not lie in the contractile proteins. It is likely, however, that the decreases in intracellular ATP and Mg2+ concentrations which occur in pigs during malignant hyperthermia, contribute to the development of the syndrome.