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Effect of Dietary Fat Level and Polyunsaturated Fatty Acid Content on the Phospholipid Composition of Rat Cardiac Mitochondrial Membranes and Mitochondrial ATPase Activity¹

Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, 150 College Street, Toronto, Ontario, Canada M5S 1A8

Weanling rats were fed either high fat diets containing 40% of calories as fat or low fat diets containing 15% of calories as fat for 14 days. All diets were formulated to contain equivalent essential nutrients per calorie content for the nonfat components. For both dietary fat levels, the polyunsaturated to saturated fatty acid (P/S) ratio was adjusted by substitution of beef tallow for soybean oil to provide a dietary P/S ratio of 2.0 or 0.25. After feeding, hearts were removed from six replicate groups of animals per diet treatment, and mitochondria were isolated. Phospholipids were extracted from the mitochondrial membranes, and cardiolipin, phosphatidyl-choline and phosphatidylethanolamine content were quantitatively analyzed using an iatroscanner. In addition, fatty acyl tail composition of each purified phospholipid was determined. Mitochondrial ATPase was also assessed by a ATP-³²P_i exchange assay. Feeding high fat diets increased phosphatidylcholine content of the mitochondrial membrane. High fat diets resulted in a relative increase in mitochondrial cardiolipin content that was apparently unaffected by the P/S ratio of the diet fed. Both the fat level in the diet and the P/S content altered ATPase activity. This study indicates that for an animal model, diets analogous in fatty acid content and composition to those potentially consumed by humans can result in alterations in membrane structural constituents of cardiac mitochondria and have the potential to alter lipid-dependent functions of integral membrane proteins.

KEY WORDS: • rat • diet • fat • membrane • ATPase

¹ This work was supported by the Ontario Heart Foundation.

Manuscript received 11 August 1983.