THE PYRETHROID INSECTICIDE DELTAMETHRIN MODIFIES THE THERMOTROPIC PROPERTIES AND LIPID PACKING ORDER OF MODEL MEMBRANES

The effects of deltamethrin on model membranes were investigated by DS C and by DPH and TMA-DPH fluorescence anisotropy. At a 5:1 phospholipi d/pyrethroid ratio the thermal transition temperature (T-m) of dimyris toyl- (DMPC), dipalmitoyl- (DPPC) and distearoyl-phosphatidylcholine ( DSPC) decreased by 3.0, 0.5 and 0.7 degrees C, respectively. Deltameth rin broadened the phase transition of DMPC, but not of DPPC or DSPC. D PH and TMA-DPH fluorescence anisotropy experiments showed that, below the T-m, deltamethrin reduced the lipid packing order, whereas above t he T-m, it induced an ordering effect. In egg-phosphatidylcholine vesi cles, deltamethrin increased the DPH, but not the TMA-DPH fluorescence anisotropy. The low solubility of deltamethrin in water prevented us for further investigating its effects on native membranes. The results suggest that deltamethrin is preferentially located in the hydrophobi c core of model membranes, where it reduces the lipid packing order in the gel stale and enhances it in the liquid-crystalline state.