Oxidation-dependent changes in the stability and permeability of lipid bilayers.

Peroxidation-dependent change in the permeability of lipid bilayers was mesaured by using artificial membrane systems, that is, planar lipid bilayers and liposomes. The unsaturated fatty acyl chains of phospholipids in small unilamellar vesicles were peroxidized time-dependently by the hydroxyl radical chemically generated by the reaction of H2O2 and Cu(en)2. In contrast, at the same hydroxyl radical concentration and time ranges, no ionic current through the planar lipid bilayers and no release of K+ from the liposomes were observed. These findings indicate that accumulation of lipid peroxide within lipid bilayers is not responsible for the permeability increase that is often observed in biomembranes exposed to oxidative stresses. Higher concentration of the hydroxyl radical caused break-down of the planar lipid bilayers composed of the mixture (7:3) of phosphatidylethanolamine (PE) and phosphatidylcholine (PC). The bilayer containing 100% PE at least at one leaflet of the bilayer (facing the hydroxyl radical-generating solution) was not broken-down by the application of the hydroxyl radical, suggesting that PE stabilizes the planar lipid bilayer against the attack of the hydroxyl radical.