Use of a Fluorescent Probe to Compare the Plasma Membrane Properties in Normal and Transformed Cells. Evaluation of the Interference by Triacylglycerols and Alkyldiacylglycerols

The fluorescent probe l,6-diphenyl-l,3,5-hexatriene (DPH) was used to study the plasma membrane properties of normal and Rous sarcoma virus transformed chicken embryo fibroblasts. When measurements were made on whole cells, the fluorescence polarization of different cell preparations showed an inverse correlation with the amount of triacylglycerols and alkyldiacylglycerols present in the cells. These neutral lipids were stored as droplets within the cell and their accumulation depended on the concentration of serum in the medium, the cell density, and the time of growth. When plasma membranes were isolated that contained negligible amounts of triacylglycerols and alkyldiacylglycerols, the fluorescence polarization of DPH in the membranes was very different from the polarization of DPH in intact cells. The changes in the polarization of the probe in intact cells under different conditions were primarily reflecting the changes in the amount of triacylglycerols and alkyldiacylglycerols. DPH in plasma membranes isolated from transformed cells had a slightly higher fluorescence polarization than in membranes from normal growing cells. DPH in total lipid extracts and phospholipids prepared from the transformed cell membranes also had a higher polarization as compared with the respective extracts from normal growing cells. The higher polarization appeared to be due to increases in the concentration of phosphatidylethanolamine and 18:1 and to decreases in the amount of polyunsaturated fatty acids. Plasma membranes and total lipid extracts prepared from confluent cells had a greater increase in the polarization of DPH when compared with normal growing cells. No difference in polarization of DPH was found, however, for the phospholipids from membranes of normal growing and confluent cells. The difference in polarization for the membranes and total lipid extracts was consistent with an increase in the cholesterol content of the confluent cells as compared with normal growing cells.