Uptake and release of calcium ions by heavy sarcoplasmic reticulum fraction of normal and malignant hyperthermia-susceptible human skeletal muscle.

1. Ca2+ uptake, Ca2(+)-dependent ATPase activity and halothane-induced Ca2+ release from the heavy sarcoplasmic reticulum fraction of muscle from malignant hyperthermia susceptible individuals are similar to those of normal human muscle. 2. Ca2(+)-induced Ca2+ release from the diseased muscle was increased by 13%.