A flash photolysis study of the formation of retinal Schiff bases in a native photoreceptor cell

Abstract

It is believed that the accumulation of all-trans-retinal (ATR) in retinal cells is responsible for photoinduced damage to the retina. However, ATR is formed within a photoreceptor cell disk in the process of photolysis and transferred to the cell cytoplasm, where it is converted in a high yield into the nonphototoxic compound retinol. Within the disk where ATR can be accumulated, retinol can form Schiff bases, which are also nonphototoxic compounds, with the amino groups of proteins and lipids. Thus, it is unclear in which concentrations free ATR can be accumulated inside a cell. In this study, it has been proposed to evaluate the concentration of free ATR in the cell from the yield of an excited triplet state because neither Schiff bases nor retinol can be transformed into an excited triplet state. It has been found that 70% ATR forms Schiff bases in the native cell in the equilibrium state, thereby, a considerably decreasing the probability that ATR is the main inducer of photodamage.