EFFECT OF FENITROTHION ON HEPATOPANCREAS MICROSOMAL MEMBRANE FLUIDITYIN MACROBRACHIUM-BORELLII

The effects of the organophosphorus insecticide fenitrothion [phosphor othioic acid, O,O-dimethyl O-(3-methyl-4-nitrophenyl) ester] on the ph ysical state of microsomal membranes from the hepatopancreas of the fr eshwater shrimp Macrobrachium borellii were investigated. Physical pro perties of native membranes and liposomes obtained from their total li pids were studied by fluorescence polarization of 1,6-diphenyl-1,3,5-h exatriene (DPH), probing the bilayer core, and by its anionic propioni c acid derivative (DPH-PA), probing the outer regions of the bilayer. Fenitrothion was found to increase DPH and DPH-PA polarization of micr osomal and liposomal membranes when added in vitro at concentrations w ithin the order of 10(-6) M. No significant effects were observed in m embranes from animals exposed to the insecticide in vivo. Nevertheless , the effect of fenitrothion on the microsomes of exposed animals is o bserved in a lesser degree than on those from control animals, suggest ing an adaptation of the membranes to fenitrothion. Considering that t his effect is lower in the liposomes of control and exposed animals, t he adaptation seems to involve the protein moiety of the membranes. Fl uorescence anisotropy lifetimes (determined by phase-shift (tau(P)) an d demodulation (tau(M)) techniques) of DPH were decreased by 0.72 mu M fenitrothion in microsomes. The limiting anisotropy of DPH is increas ed in native membranes that contain fenitrothion, indicating a further ordering effect. (C) 1997 Academic Press.