Dietary induction of acyl chain desaturases alters the lipid composition and fluidity of rat hepatocyte plasma membranes

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Abstract
Rats were maintained on a regimen of intermittent starvation followed by refeeding a fat-free diet in order to induce hepatic acyl desaturase activities and other enzymes involved in lipid synthesis. The effects of the dietary regimen on the lipid composition and fluidity of isolated hepatocyte plasma membranes were compared to corresponding effects on microsomal preparations. The dietary regimen increased the content of monoenoic and polyenoic acyl chains, and decreased the cholesterol/phospholipid molar ratio in the plasma membranes. Accordingly, the lipid fluidity of the plasma membranes was significantly increased as assessed by the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene and 12-(9-anthroyloxy)stearate and the intramolecular excimer fluorescence of 1,3-di(1-pyrenyl)propane. In the microsomal membranes, substantial increases in the content of monoenoic acyl chains were offset by decreases in polyenoic acids and no change in cholesterol/phospholipid ratio was observed. The lipid fluidity of the microsomal membranes remained almost unchanged. The enhancement of lipid fluidity in the hepatocyte plasma membranes was accompanied by an increase of .apprx. 68% in the specific activity of the (Na+ + K+)-dependent ATPase. A dietary regimen can modulate in vivo the lipid composition, fluidity and enzyme function of the hepatocyte plasma membrane.