Electric breakdown of bilayer phospholipid membranes under ultraviolet irradiation-induced lipid peroxidation.

Lipid peroxidation (LPO) of unsaturated fatty acids in bimolecular lipid membranes (BLM), induced by ultraviolet irradiation [l-3] or by chemical agents [4], brings about an increase in conductivity of these membranes. For BLM prepared from egg phosphatidylcholine/cholesterol mixture this effect is accounted for by the rise of proton permeability [3,5]; the maximal conductivity enhancement being <2-3-times higher as compared to the initial level [3]. In contrast with this case, BLM prepared from brain phospholipids [2] exhibited a much more pronounced effect: the conductivity rise was sharp and reached several orders of magnitude. In the light of the observation that ultraviolet-induced LPO reduces BLM electric stability (the measure of which can be the ‘breakdown’ potential) [6], one may assume that the electric instability contributes significantly to the observed ‘high amplitude’ increase in BLM conductivity caused by LPO. In the LPO reaction a great variety of products is produced [7] and the secondary products of LPO are found to be the most effective in the activation of BLM ionic conductivity [ 11. But the precise mechanism by which these substances influence the electric properties of lipid membranes is still to be unravelled. It is the purpose of this paper to estimate the contribution of electric breakdown to the LPOinduced increase in the ionic permeability of BLM and the involvement of charged LPO products into this process. 2. Materials and methods