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Ca²⁺-Mg²⁺ ATPase of Mouse Cardiac Sarcoplasmic Reticulum is Affected by Membrane n-6 and n-3 Polyunsaturated Fatty Acid Content¹

Lipids Research Laboratory, Institute of Food Science, Cornell University, Ithaca, NY 14853

White mice, 18–20 g, were fed purified diets containing two weight percent safflower oil plus ten weight percent menhaden, corn, or olive oil for 2 wk. Menhaden oil ingestion resulted in significantly higher levels of 22:6(n-3) and 20:5(n-3), particularly 22:6(n-3), and lower levels of 20:4(n-6) and 18:2(n-6) in cardiac sarcoplasmic reticulum (SR) phospholipids than did corn or olive oil ingestion. These changes in fatty acid composition resulted in a significant decrease in the value of the n-6/n-3 fatty acid ratio of cardiac SR phospholipids. The ratio was 2.8 versus 0.2 in choline phospholipids and 1.9 versus 0.2 in ethanolamine phospholipids in SR of mice fed corn or menhaden oil, respectively. This reduction in the n-6/n-3 fatty acid ratio was associated with a lower relative activity of Ca²⁺-Mg²⁺ ATPase, and a lower initial rate of calcium transport and maximum calcium uptake in SR vesicles from mice fed menhaden oil rather than olive or corn oils. The specific activity of NADPH cytochrome C reductase (EC 1.6.2.3) of cardiac SR was not affected by dietary lipids. These data indicate that modification of SR by 22:6(n-3) may change the SR bilayer structure resulting in alteration of the calcium transport properties of SR vesicles. In addition, our results suggest that reduction of calcium flux across cardiac SR following fish oil consumption may also reduce the susceptibility of myocytes to rapid changes in calcium concentrations which may occur during ischemia and reperfusion.

KEY WORDS: • fish oils • heart lipids • calcium transport • Ca²⁺-Mg²⁺ ATPase • NADPH cytochrome C reductase • n-3 polyunsaturated fatty acids

¹ Funded in part by the New York SeaGrant program and United States Department of Agriculture nutrition grant 86-CRCR-1-1086.

² Current address: Department of Biochemistry, Molecular and Cell Biology, Clark Hall, Cornell University, Ithaca, NY 14853.

Manuscript received 5 April 1988. Revision accepted 27 October 1988.

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