Deficient function of the sarcoplasmic reticulum in patients susceptible to malignant hyperthermia.

Calcium uptake and (Ca2+ + Mg2+)-ATPase were measured in sarcoplasmic reticulum (SR) vesicles prepared from muscles of eight patients susceptible to malignant hyperthermia (MH) and eight control subjects. Intracellular resting free calcium level of some of the studied subjects was also determined. Both calcium uptake capacity and (Ca2+ + Mg2+)-ATPase activity were significantly lower in SR prepared from MH-susceptible patients than from normal subjects. Besides, in these MH-susceptible patients myoplasmic free Ca2+ was increased. These results corroborate previous suggestions that abnormal function of the SR membrane was related to the MH syndrome.