Oxygen as an inductor of divalent cation permeability through biological and model lipid membranes

The action of lipid hydroperoxides (LH), which are primary products of lipid oxidation, on cation permeability through bilayer lipid membranes (BLM) and sarcoplasmic reticulum (SR) membranes was investigated. Bilayer lipid membranes prepared from unoxidized phosphatidyl choline (PC) plus cholesterol or from total phospholipids extracted from SR vesicles possessed low cation permeability. Lipid oxidation induced by Fe2+-ascorbate led to a sharp increase in the calcium current through the BLM and to a considerable increase in the concentration of LH products. Further spontaneous lipid oxidation to final products led to decrease of LH concentration and calcium current through the BLM. The Ca2+ conductivity of the BLM increased more strongly if Fe2+-ascorbate was added to both sides of the BLM. The LH-induced cation permeability decreased in the sequence Ca2+, Mg2+, Ba2+, Sr2+, K+, Rb+, Cs+, NH4+, Na+, Li+. This is similar to the order of cation permeability known as the biological row of permeability and holds for BLMs formed from various lipids. In addition, Fe2+-ascorbate induced calcium ion leakage from SR vesicles isolated from guinea pig heart or from rabbit white skeletal muscle. It is proposed that the lipid hydroperoxide molecules form the simplest channel in lipid membranes, providing the permeability for calcium and other divalent cations.