Changes in muscle lipid composition and resistance adaptation to temperature in the freshwater crayfish, Austropotamobius pallipes.

The phospholipid and fatty acid composition of muscle lipid extracts from crayfish acclimated to 4 C and 25 C (18 hr-light photoperiod) were analyzed. The phospholipid content and class distribution, and cholesterol content were unaffected by the acclimation treatment. Unsaturation of muscle phosphoglycerides was higher in cold acclimated crayfish. Serine/inositol phosphoglycerides from cold-acclimated animals showed somewhat higher proportions of mono- and polyunsaturated fatty acids, whereas choline and ethanolamine phosphoglycerides were less affected. This was correlated with a decreased resistance of cold-acclimated crayfish to lethal high temperature. Acclimation at 4 C under an 8 hr-light photoperiod caused an increased fatty acid unsaturation of the total phospholipid fraction compared to the 4 C, 18 hr-light photoperiod acclimated animals. The resistance of 4 C acclimated crayfish to lethal high temperature, however, was unaffected by daylength treatment. The resistance of freshwater crayfish to lethal high temperature is not simply related to the degree of saturation of the muscle phospholipids. It is suggested that a breakdown in the integrity of a bulk-lipid bilayer is not involved in the process of heat death; rather, that a membrane-bound protein factor, whose thermal sensitivity is modified by changes in its phospholipid environment during temperature adaptation but not during photoperiod adaptation, is the primary site of heat injury.