Lack of a Correlation between Hyperthermic Cell Killing, Thermotolerance, and Membrane Lipid Fluidity

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Abstract
Butylated hydroxytoluene (BHT) is an effective membrane lipid perturber. Uptake studies using [3H]BHT showed that it is effectively taken up by V79 Chinese hamster lungs cells. The correlation time of rotation (.tau.c) of the spin label 2,2-dimethyl-5-dodecyl-5-methyloxazolidine-N-oxide (2N14) was decreased 4.0 and 12.9% by addition of 0.03 and 0.07 mM BHT, respectively. This corresponds to increases in membrane fluidity produced by temperature increases of 1.8 and 6.0.degree. C, respectively. Neither BHT treatment sensitized the cells to hyperthermia. Also no decrease in membrane lipid fluidity, again as measured with the spin label 2N14, was found in thermotolerant V79 cells compared to control cells. Thermotolerance was induced by a 20 min exposure to 44.5.degree. C and the membrane fluidity measurements were made 16 h later, when the maximum level of thermotolerance was observed. Thus no evidence was found for a correlation between membrane lipid fluidity and hyperthermic killing of V79 cells.