Fluorescence polarization measurements on normal and tumour cells and their corresponding plasma membranes

Abstract

Using 1,6-diphenyl-1,3,5-hexatriene as a probe, the degree of fluorescence polarization ( P) at 25°C of intact and disrupted cells and isolated plasma membranes were compared for a variety of systems. 1. 1. Human erythrocytes, mouse thymocyte and leukemia cells, rat liver and hepatoma cells, and human and mouse milk fat globules displayed P values ranging from 0.300 to 0.120. 2. 2. P values or probe labelling rates of intact and disrupted cells were similar. 3. 3. As compared with whole or disrupted cells, the higher to much higher P values of plasma membranes isolated from the corresponding cells showed only a limited mutual variation. 4. 4. ΔP values, being the difference in P values between plasma membranes and whole cells were attributed to the extent to which endomembranes and non-membrane lipids contributed. Among these, triglycerides had the greatest relative effect. 5. 5. Though a particular isolation procedure for plasma membranes may select for more rigid fragments, this effect is by far not sufficient to account for the observed ΔP values. It is concluded that the fluorescence polarization technique with a lipophilic probe applied to whole cells represents a measure of the average fluidity of all lipids being present in a cell and thus does not exclusively monitor the cell surface membrane.