[Study of mechanisms of photoreceptor membrane destabilization under modifying action of oxygen]

Induction of lipid peroxidation in the rod outer segments (ROS) of frog retina results in fragmentation of photoreceptor disc membranes and solubilization of lipoprotein rhodopsin complexes (sedimentation coefficient 2.7S). The substrates of lipid autooxidation are mainly docosahexa- and docosapentaenoyl residues of phosphatidyl ethanolamine. Large fragments (precipitation at 5000 gX30 min) and small vesicles (precipitation at 40 000 gX60 min; average diameter 1000 A) formed from lipoperoxidized ROS differ both in their chemical composition and structural organization. In small vesicles the content of O2-modified polyenoic acyls in the phospholipids is 3,7 times higher as compared to large fragments. Correspondingly, the capacity of hydrophobic areas in the small vesicle membranes evaluated by EPR spin-probing technique is lower than in the large fragments. A mechanism of the photoreceptor membrane destabilization under modification by molecular oxygen is proposed. It is based on a decrease in the value of surface tension upon accumulation of lipid peroxidation products in ROS, the former possessing the properties of non-ionic detergents.