Effect of Fenitrothion on Hepatopancreas Microsomal Membrane Fluidity inMacrobrachium borellii

Abstract

The effects of the organophosphorus insecticide fenitrothion [phosphorothioic acid,O,O-dimethylO-(3-methyl-4-nitrophenyl) ester] on the physical state of microsomal membranes from the hepatopancreas of the freshwater shrimpMacrobrachium borelliiwere investigated. Physical properties of native membranes and liposomes obtained from their total lipids were studied by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), probing the bilayer core, and by its anionic propionic acid derivative (DPH–PA), probing the outer regions of the bilayer. Fenitrothion was found to increase DPH and DPH–PA polarization of microsomal and liposomal membranes when addedin vitroat concentrations within the order of 10−6M. No significant effects were observed in membranes from animals exposed to the insecticidein vivo.Nevertheless, the effect of fenitrothion on the microsomes of exposed animals is observed in a lesser degree than on those from control animals, suggesting an adaptation of the membranes to fenitrothion. Considering that this effect is lower in the liposomes of control and exposed animals, the adaptation seems to involve the protein moiety of the membranes. Fluorescence anisotropy lifetimes (determined by phase-shift (>P) and demodulation (>M) techniques) of DPH were decreased by 0.72 μM fenitrothion in microsomes. The limiting anisotropy of DPH is increased in native membranes that contain fenitrothion, indicating a further ordering effect.