Effect of dietary modulation of membrane lipid composition on the thermostability of HTC cells and of a membrane enzyme.
Growth of hepatoma tissue culture (HTC) cells in the presence of linoleic (18:2) or arachidonic (20:4) acids for 36 h caused an increased cell thermosensitivity. Plasma membrane-rich fractions were purified (15-20-fold) with high yield (30%) from control and fatty acid-supplemented cells. Contamination with membranes from mitochondria, lysosomes and endoplasmic reticulum was low. Supplementation significantly increased the level of the supplemented fatty acid and decreased the level of oleic acid (18:1) in plasma membrane phospholipids (PL), causing a significant decrease in the oleic acid:PUFA (polyunsaturated fatty acid) ratio. No significant changes occurred in other parameters such as cholesterol:PL, cholesterol:protein or PL:protein ratios. Plasma membranes from PUFA-supplemented cells exhibited a lower membrane order, compared with control cell membranes, as determined by DPH fluorescence polarization over the temperature range 4-40 degrees C. Isothermal inactivation of alkaline phosphodiesterase I in plasma membranes from control and supplemented cells showed curvilinear kinetics. The change in membrane composition and order following supplementation with arachidonic acid was associated with increased thermosensitivity of this enzyme. These data are discussed with respect to the suggestion that the plasma membrane may be a target for cellular thermal injury and death.
Department of Biological Sciences, University of Durham, Durham City, UK.
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Ladha
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Kingston
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Manning
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Bowler
D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004795:Enzyme Stability; D006358:Hot Temperature; D006979:Hyperthermia, Induced; D007700:Kinetics; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000494:pharmacology; D008114:Liver Neoplasms, Experimental / Q000378:metabolism* / Q000628:therapy; D008563:Membrane Lipids / Q000378:metabolism*; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D008041:Linoleic Acids; D008563:Membrane Lipids; D016718:Arachidonic Acid; D019787:Linoleic Acid; D010727:Phosphoric Diester Hydrolases; D043264:Phosphodiesterase I