Retinal Sensitized Photodynamic Damage to Liposomes

All trans‐retinal has been introduced (2 mol %) into artificial membranes made up of egg lecithin, cholesterol and dicetyl phosphate. Illumination of retinal‐enriched liposomes at 365 nm induced photodynamic damages; it triggered the sensitized oxidation of the lipids measured by the appearance of a 233 nm absorption band or by the formation of malonyl dialdehyde. Illumination produced an increase of the membrane fluidity detected with the spin label technique and led also to the lysis of the liposomes as revealed by the release of entrapped chromate ions or by changes in light scattering. Singlet oxygen is involved in these photodynamic effects. The results have been discussed in connection with the light damage phenomena which may afflict the rod outer segment membranes.