FLUIDITY OF LM CELL-MEMBRANES WITH MODIFIED LIPID COMPOSITIONS AS DETERMINED WITH 1,6-DIPHENYL-1,3,5-HEXATRIENE

The fluorescence polarization and lifetime of 1, 6-diphenyl-1, 3, 5-hexatriene (DPH) were determined from 5 to 40 °C in mitochondrial, microsomal, and plasma membranes isolated from LM cells grown in tissue culture. The rotational relaxation times of DPH calculated from these measurements were highest in plasma membranes and lowest in mitochondrial membranes. Approximately the same ratios of the rotational relaxation times for the three membranes were maintained throughout the temperature range. The phospholipid polar head group composition of the membranes was altered by substituting ethanolamine for choline in the growth medium. Likewise, the fatty acid composition was altered by adding linoleate to the growth medium. These changes in the lipid composition produced an increase and a decrease, respectively, in the rotational relaxation times of DPH in all three membrane fractions. Nevertheless, approximately the same ratios of the rotational relaxation times of DPH were maintained between the different membranes. This suggests that this parameter is closely regulated. Examination of the rotational relaxation times of DPH in whole lipid and phospholipid dispersions prepared from the isolated membranes indicated that the observed differences could be explained by differences in the sterol, fatty acid, and polar head-group compositions. Changes in the sterol content and the phospholipid composition both contributed substantially to the changes produced in the rotational relaxation times. © 1979, American Chemical Society. All rights reserved.