The Organophosphorus Insecticide Parathion Changes Properties of Natural and Model Membranes

The interaction of parathion, a widely used organophosphorus insecticide, with cell membranes of the isolated toad skin, human erythrocytes, and membrane molecular models is described. The latter consisted of multilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) and large unilamellar vesicles (LUV) of DMPC. They represent phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. Results obtained from electrophysiological measurements of the toad skin supported the deduction that the main site with which parathion interacted to reduce ion transport is situated on the outward facing barrier of the epithelium. Fluorescence spectroscopy showed that the insecticide interacted with and altered the structure of isolated unsealed human erythrocyte membranes. The increase of the fluorophor DPH anisotropy and of laurdan general polarization indicated an ordering effect on the acyl chains and a decrease in the molecular dynamics and/or water penetration at the lipid polar head group region. However, in DMPC LUV parathion at increasing concentrations enhanced the polar head group ordering but decreased that of their acyl chains. X-ray analysis of DMPC and DMPE multilayers showed that both structures were deeply perturbed by a parathion:lipid ratio as low as 1:200. Nonetheless, increasing parathion concentrations induced A different results in both lipid bilayers.