Porcine malignant hyperthermia: effects of temperature and extracellular calcium concentration on halothane-induced contracture of susceptible skeletal muscle.

Skeletal muscle from malignant hyperthermic (MH) pigs incubated at 37 C in 2.3 mM calcium-Krebs-Ringer solution contracts spontaneously when exposed to halothane. In contrast, halothane did not induce contracture in MH muscle incubated in 2.3 mM calcium-Krebs-Ringer solution at 25 C or in calcium-free Krebs-Ringer's solution at 37 C. Halothane did not induce contracture in normal control muscle in 2.3 mM Krebs-Ringer solution at 25 or 37 C. In the presence of halothane, addition of caffeine produced greater contracture in MH muscle than in normal controls. Halothane-caffeine-induced contractures of MH and control muscles at 25 and 37 C were similar. Elucidation that under certain experimental conditions halothane induces contracture in MH muscle, but not in normal muscle 1) may aid in development of a diagnostic test; 2) establishes further evidence for skeletal muscle as the target tissue for anesthetic-induced MH; 3) suggests that halothane may affect systems that regulate sarcoplasmic calcium concentration below contracture threshold in MH muscle. (Key words: Hyperthermia, malignant; Anesthetics, volatile, halothane; Ions, calcium; Muscle, skeletal, malignant hyperthermia.).