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E. T. Villazana-Espinoza, A. L. Hatch, A. Muniz, A. T. C. Tsin; Activity of Retinol Isomerase, Ester Synthase and Retinol Dehydrogenase in the Isolated Chicken Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3243.
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Direct evidence of a light-driven cone cycle in the chicken retina was recently obtained and reported by our laboratory. This novel retinoid cycle utilizes 11-cis retinyl esters in the retinas as the primary source of visual chromophore for cone pigment regeneration. The purpose of this study is to investigate cone cycle pathway in the isolated chicken retina.
Chicken eyes were dark adapted for two hours before the anterior segment, lens, and vitreous were removed under dim light. The retina was dissected from the eye cup and placed in a test tube containing all-trans retinol (5µl in DMSO, 9.9 nm) or 11-cis retinol (5µl in DMSO, 3.9nm) with 133µg IRBP in MEM, in a final volume of 100µl and exposed to light (2,000 Lux incandescent ) at 4°C for 30 minutes. To stop the reaction, 1ml of avian buffer at 4°C was added. Retinoids were extracted and analyzed via HPLC. Experiments were repeated 4 times with similar results.
Upon light adaptation, 11-cis retinyl esters and all-trans retinyl esters increased from 0.13 to 0.71, and from 0.02 to 0.29 nmol/mg, respectively. Similarly, 11-cis retinol and all-trans retinol also increased from 0.02 to 0.12, and from 0.03 to 1.10 nmol/mg, respectively in response to light. Meanwhile, 11-cis retinal decreased in the light from 0.05 to 0.0007 and all-trans retinal increased from 0.007 to 0.05 nmol/mg, in response to light. .
Upon light exposure, chicken retina converts exogenous all-trans retinol to 11-cis retinol, 11-cis retinyl ester and all-trans retinyl esters. Chicken retina also converts 11-cis retinol to 11-cis retinal. Based on the accumulation of different retinoids in our experiment, we conclude that the isolated chicken retina contains retinol isomerase, retinol dehydrogenase and retinyl ester synthase activity in support of the cone visual cycle in the retina.
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