TOTAL CALCIUM CONTENT OF SKELETAL MUSCLE ISOLATED FROM HUMANS AND PIGS SUSCEPTIBLE TO MALIGNANT HYPERTHERMIA

Total calcium content of both human and porcine MHS skeletal muscle is significantly less than normal. This data is consistent with the concept that some organelle (prob-ably the sarcoplasmic reticulum, the mitochondrion or even the sarcolemma) within the MHS muscle stores less than normal amounts of calcium. The large variability between muscle specimens rules out measurement of total calcium content of skeletal muscle as a routine diagnostic test for malignant hyperthermia susceptibility. Malignant hyperthermic susceptible (MHS) muscle has been postulated to be less capable than normal of storing calcium within some organelle or membrane. The defective organelle might be the sarcoplasmic reticulum (SR) (Britt et al., 1973; Kalow et al., 1970), the mitochondrion (Britt et al., 1974) or even the sarcolemma (Gordon, Britt and Kalow, 1973). If such an organelle did contain less than normal quantities of calcium, one would expect that the total calcium content might also be less than normal. Therefore we decided to measure the total calcium content of vastus lateralis muscle obtained from normal and MHS humans and swine. METHODS Anaesthetic and surgical techniques. Pigs. The swine used were either normal York pigs of MHS York/Poland-China hogs. Suscepti-bility of the latter pigs was assured by: (a) a posi-tive isometric muscle contracture test (Britt et al., 1973, 1974; Kalow et al., 1970); and (b) a subse-quent halothane-induced hyperthermic rigor. The animals were premedicated with diazepam (Valium) 4 mg/kg i.m. Anaesthesia was maintained with oxygen in nitrous oxide and diazepam as required. A field block of procaine 1 % (without adrenaline) was infiltrated around, but not into, the biopsy site. One-and-a-half gram of muscle was excised from the vastus lateralis. All possible fascia and fat were cut away from the muscle before severing its blood supply. The excised muscle was immediately frozen in liquid nitrogen. The frozen muscle wa