Intracellular ionized calcium concentration in muscles from humans with malignant hyperthermia

Ca²⁺ selective microlectrodes have been used to determine the free myoplasmic [Ca²⁺] in human skeletal muscle obtained from patients who had developed early signs associated with malignant hyperthermia (MH) during anesthesia. Intercostal muscle biopsies were performed under local anesthesia in four MH patients 15 days to 4 months after developing the MH crisis and in three control subjects. We used only microelectrodes that showed a Nernstian response between pCa₃ and pCa₇ (30.5 mV per decade at 37°C). Membrane resting potential (V_m) and calcium potential (V_Ca) were obtained from superficial fibers. The free cytosolic [Ca²⁺] was 0.39 ± 0.1 m̈M (mean ± SEM, n = 18) in muscle fibers obtained from malignant hyperthermic patients, whereas in control subjects it was 0.11 ± 0.02 m̈M (n = 10). These results suggest that this syndrome might be related to an abnormally high myoplasmic free resting calcium concentration, probably due to a defective function of the plasma membrane or the sarcoplasmic reticulum.