Calcium ATPase in the sarcoplasmic reticulum of muscle from normal and malignant hyperthermia susceptible pigs

The density of Mg 2+-dependent Ca 2+ ATPase in the terminal cisternae of pig skeletal muscle fibres was investigated to discover whether a reduction in Ca 2+ ATPase content impairs Ca 2+ sequestration and contributes to the elevated myoplasmic Ca 2+ concentration in malignant hyperthermia. Unexpectedly, immunogold electron microscopy showed an increase in Ca 2+ ATPase, while densitometry of SDS-polyacrylamide gels suggested that the Ca 2+ ATPase content of terminal cisternae vesicles did not change. The affinity of Ca 2+ ATPase in vesicles for our monoclonal antibody was not altered. We suggest that the availability of antigenic sites in malignant hyperthermia increases after processing for electron microscopy, perhaps as a consequence of altered sarcoplasmic reticulum membrane properties.