Membrane fluidity as affected by the insecticide lindane

Abstract

Fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) was used to study the interaction of lindane with model and native membranes. Lindane disorders the gel phase of liposomes reconstituted with dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines (DMPC, DPPC and DSPC), since it broadens and shifts the main phase transition, but no apparent effect is detected in the fluid phase. These effects of lindane are more pronounced in bilayers of short-chain lipids, e.g., DMPC. In equimolar mixtures containing DMPC and DSPC, lindane preferentially interacts with the more fluid lipid species inducing lateral phase separations. However, in mixtures of DMPC and DPPC, the insecticide only broadens and shifts the main phase transition, i.e., an effect similar to that observed in bilayers of pure lipids. Lindane has no apparent effect in DMPC bilayers enriched with high cholesterol content (greater than or equal to 30 mol%), whereas disordering effects can still be detected in bilayers with low cholesterol (less than 30 mol%). Apparently, lindane does not perturb the fluid phase of representative native membranes, namely, mitochondria, sarcoplasmic reticulum, myelin, brain microsomes and erythrocytes in agreement with the results obtained in fluid phospholipid bilayers, despite the reasonable incorporation of the insecticide in these membranes, as previously reported (Antunes-Madeira, M.C. and Madeira, V.M.C. (1985) Biochim. Biophys. Acta 820, 165-172).