ANALYSIS OF LIPID-COMPOSITION OF SARCOPLASMIC-RETICULUM MEMBRANES FROM NORMAL AND MALIGNANT HYPERTHERMIC PIG SKELETAL-MUSCLE

In search of a general membrane defect hypothesis for malignant hyperthermia syndrome, we analysed the lipid profiles of heavy sarcoplasmic reticulum membranes isolated from normal and malignant hyperthermia longissimus dorsi pig muscle. Malignant hyperthermia susceptibility was assessed by halothane challenge of pigs. Sarcoplasmic reticulum membranes from malignant hyperthermia susceptible pigs differed significantly from control ones in the cholesterol content and phosphatidylethanolamine/phosphatidylcholine ratio; both were higher in former membranes. These latter lipid modifications were in agreement with the significant increase of their bulk lipid viscosity, as evidenced by an increase of diphenyl hexatriene fluorescence anisotropy. The increased level of phosphatidylethanolamine associated with the decreased content of phosphatidylcholine in malignant hyperthermic membranes was shown to be a potential consequence of depressed activities of both phospholipid N-methyltransferase I and II activities. Finally, the distribution of fatty acids in these particular phospholipids showed no change in phosphatidylcholine molecules, whereas the percentage of arachidonate and stearate in the phosphatidylethanolamine species were respectively higher and lower in malignant hyperthermic membranes. These differences in major phospholipids content and the enrichment of a metabolically important fatty acyl chains in malignant hyperthermia sarcoplasmic reticulum membranes strongly suggest that the lipid metabolism may contribute to the molecular mechanism of malignant hyperthermia syndrome.