Effect of Dietary Fatty Acids on Ca2+-ATPase Activity of the Sarcoplasmic Reticulum of Rainbow Trout Skeletal Muscle

Abstract

Effects of different dietary lipids, corn oil, cod liver oil, and beef tallow, on lipid compositions and Ca2+-ATPase activity of the rainbow trout Salmo gairdneri sarcoplasmic reticulum (SR) were examined. The levels of phosphatidylethanolamine (PE) of the muscle and the SR were lower in fish fed for 2 months on diets rich in n-6 fatty acids or deficient in polyunsaturated fatty acids (PUFA) than in those fed n-3 fatty acid rich diet. Fatty acid compositions of muscle well reflected those of the diets. On the other hand, the SRs contained higher levels of polyunsaturated fatty acids, such as 22:6n-3, than muscle. In particular, PE fractions of each SR exhibited very high contents of polyunsaturated fatty acids and feeding PUFA-deficient diet for 3 months failed to reduce markedly the level of 22:6n-3 in PEs. Fatty acid compositions of phosphatidylcholine (PC) fractions of the SRs were altered by dietary fatty acids more easily than those of PEs. n-3 Fatty acid rich diet feeding caused reduction of SR Ca2+-ATPase activities. There was hardly any difference in peptide mapping patterns of Ca2+-ATPase proteins through the experimental stages, suggesting that there was practically no change of the Ca2+-ATPase moiety itself in the primary structure. These results suggested that dietary fatty acid compositions would alter lipid class and fatty acid compositions of the rainbow trout SRs and consequently lipid conformation changes. It was concluded that such physiological changes in lipids might affect the SR Ca2+-ATPase activities.