Membrane lipid modification of chinese hamster ovary cells. Thermal properties of membrane phospholipids.

A simple and reproducible method for altering the acyl chain composition of Chinese hamster ovary cell phospholipids is described. By supplementation of the medium with 5% delipidized serum and 12 pg/ml of various fatty acids, extensive incorporation of the added fatty acid into membrane phospholipids was obtained. No significant changes in the phospholipid head group composition or the sterol/phospholipid ratio were detected during the experimental time course. Analysis of the thermal properties of these supplemented phospholipids is also described. The onset of formation of a “solid” lipid phase was detected using the fluorescent fatty acid probe, trans-parinaric acid. The temperature of onset of the solid lipid phase in extracted phospholipids was correlated with the percentage of unsaturated fatty acids esterified to the phospholipids. Fluorescence polarization measurements with cisand trans-parinaric acid in the phospholipids indicated that the amount of solid phase lipid was significantly greater in palmitate-supplemented cells than in unsupplemented or oleate-supplemented cells. The polarization analysis also indicated that the amount of solid phase lipid was approximately equal in unsupplemented and oleate-supplemented cells. Analysis of purified phosphatidylcholine and phosphatidylethanolamine from oleateand palmitate-supplemented cells indicated that the onset of solid formation in these phospholipids occurred at approximately the same temperature as the onset in the total phospholipid extract.