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M. Kono, R. K. Crouch, M. C. Cornwall, P. Ala-Laurila; 11-cis Retinol is a Suitable Substrate for Cone Pigment Regeneration. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3527.
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To determine if 11-cis retinol is a viable substrate for pigment formation in cone photoreceptors.
Human and salamander cone and rod opsins were expressed in COS cells. Effects of 11-cis retinol on opsin activity were assessed by measuring transducin activation after addition of 11-cis retinol (dark and light). Single red and blue cone photoreceptor cells were isolated from larval tiger salamander retinas and microspectrophotometry was used to monitor absorbance properties of the cells before and after bleaching the native visual pigment and addition of 11-cis retinol.
11-cis Retinol acts as an inverse agonist with red/green cone opsins and has no effect on the activity of blue cone opsins. In contrast, with rod opsin, 11-cis retinol acts as an agonist. In isolated salamander cells, pigment formation was observed in both the red and blue salamander cones suggesting that cone cells can readily oxidize 11-cis retinol. However, there is no pigment formation in the salamander red or green rods, under the same conditions.
Cones have a mechanism for handling retinoids which is different from that of rods. 11-cis Retinol activates red rod opsin and does not form a pigment. Therefore, it is not a useful substrate for rod function. However, 11-cis retinol does not activate cone opsins, and we demonstrate that cones, but not rods, can oxidize 11-cis retinol to retinal to regenerate cone pigment. A visual cycle for cones that supplies 11-cis retinol instead of 11-cis retinal is reasonable.
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