Microscopic Observations of Muscle from Swine Susceptible to Malignant Hyperthermia

Light and electron microscopic observations were made on muscle from pigs classified as malignant hyperthermia (MH) susceptible by their reaction to halothane anesthesia. Littermate MH resistant pigs served as controls. Both the lateral biceps femoris and the longissimus muscle of MH susceptible pigs contained a higher (P<.05) proportion of cells with supercontractions (30.1%) than did muscle from resistant animals (7.6%). The longissimus muscle of MH susceptible pigs also contained a higher percentage of internal (central) nuclei than did the other muscles sampled. Muscle of MH susceptible animals did not differ from control muscle in other histological and ultrastructural features.