Differential effects of environmental chemicals on liposomal bilayers. Fluorescence polarization and pesticide-lipid association studies.

The thermal dependence of the fluorescence polarization of 1,6-diphenylhexatriene was recorded upon interaction of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and some other pesticides with dipalmitoylphosphatidylcholine liposomes. Differential effects on the gel-crystalline phase were observed. Most substances decreased probe polarization; pentachlorophenol caused an increase of this parameter. The DDT-induced change of polarization was also dependent on the vesicle concentration thus indicating the influence of light scattering. The amount of DDT and pentachlorophenol residing in the lipid bilayer was determined to confirm the localization in the membrane. Correlation with the effects on probe polarization was obtained. The difference in response of the fluorescent probe to the presence of foreign molecules in the lipid bilayer may reflect different modes of interaction.