Distinct immunopeptide maps of the sarcoplasmic reticulum Ca²⁺ release channel in malignant hyperthermia

Sarcoplasmic reticulum isolated from malignant hyperthermia-susceptible (MHS) muscle exhibits abnormalities in the regulation of calcium release. To identify the molecular basis of this abnormality, the Ca²⁺ release channel from both normal and MHS sarcoplasmic reticulum was examined using proteolytic digestion followed by immunoblot staining with a polyclonal antibody against the rabbit Ca²⁺ release channel protein. Under appropriate conditions, trypsin digestion of isolated sarcoplasmic reticulum vesicles from the two types of pigs revealed a distinct difference in the immunostaining pattern of the Ca²⁺ release channel-derived peptides. An approximate 86-kDa peptide was the predominant fragment in normal sarcoplasmic reticulum while an approximate 99-kDa peptide fragment was the major peptide detected in MHS sarcoplasmic reticulum. Digestion of sarcoplasmic reticulum vesicles isolated from four normal and four MHS pigs showed that the differences were highly reproducible. Trypsin digestion of sarcoplasmic reticulum isolated from heterozygous pigs, which contain one normal and one MHS allele, showed an antibody staining pattern that was intermediate between MHS and normal sarcoplasmic reticulum. These results can be explained by a primary amino acid sequence difference between the normal and MHS Ca²⁺ release channels and support the hypothesis that a mutation in the gene coding for the sarcoplasmic reticulum Ca²⁺ release channel is responsible for malignant hyperthermia.