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B.S. Winkler, C.A. Starnes, R.G. Pourcho, D.K. Vaughn; Vulnerability of Rods and Cones to Oxidant Stress May Be Linked to Low Levels of Glutathione . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1676.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Glutathione (GSH) is a major cellular antioxidant. This study examines the immunocytochemical distribution of this critical antioxidant in rod–dominant and cone–dominant retinas and the effects of oxidative stress. Methods: For immunocytochemistry, rat, mouse, rabbit, guinea pig and ground squirrel eyecups were fixed for 2 h in 2.5% glutaraldehyde in PBS at room temperature. After fixation, the eyecups were embedded in epoxy and sections were probed with a polyclonal rabbit anti–GSH (1:100). To assess effects of oxidative stress, rat eyecups and isolated rat retinas were incubated for two hrs in oxygenated, bicarbonate–buffered media of normal ionic composition in the presence and absence of hydrogen peroxide. Measurements were made of the activity of glyceraldehyde–3–phosphate dehydrogenase (G3PDH), a glycolytic enzyme sensitive to oxidation by peroxide, and the rate of aerobic lactic acid production, an indicator of retinal energy metabolism. Results: The immunocytochemical studies showed that GSH was undetectable (less than 40 micromolar) in outer and inner segments of cones in the ground squirrel retina and of rods in rat, mouse, guinea pig and rabbit retinas. In contrast, intense label for GSH was observed in the inner retinal layers, including the ganglion cell layer, the inner plexiform layer and the inner nuclear layer in all species. Incubation of rat eyecups in media containing 1 mM hydrogen peroxide did not alter the activity of G3PDH or the rate of glycolysis in comparison to control activities. In contrast, when isolated rat retinas were incubated in media containing peroxide, the activity of G3PDH was inhibited by 40% and the rate of lactic acid production was decreased by 30%. Conclusions: We conclude that the low to absent levels of GSH in rods and cones may account for the increased suseptibility of these cells to oxidation. The inability of peroxide to produce damage in rat eyecups is most likely related to its detoxification by inner retinal neurons as it diffuses into the retina from the vitreal surface. In contrast, the deleterious biochemical effects of peroxide observed in the isolated retina are likely due to the direct access of peroxide to the photoreceptor cells. The low level of GSH in photoreceptors may also provide an explanation for the classical finding of Werner Noell that iodoacetate selectively destroys photoreceptors; detoxification of iodoacetate, like detoxification of peroxide, is GSH–dependent.
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