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Shinya Sato, Vladimir J Kefalov; Cis retinol oxidation and pigment regeneration in cone photoreceptors.. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
The canonical retinal pigment epithelium (RPE) visual cycle provides rods and cones with 11-cis retinal. A second visual cycle involving the Müller cells in the retina provides chromophore selectively to cones. However, the putative all-trans retinol isomerase of this retina visual cycle, DES1, produces preferably 9-cis over 11-cis retinol in vitro. The nature of the chromophore actually provided to cones by the retina visual cycle is unknown. Here, we sought to identify the isoform of cis retinol provided to cones by retinal Müller cells and the location of its subsequent oxidation within cones.
Salamander rods and cones were dark-adapted in the intact eye (by both the RPE and retina visual cycles), in the isolated retina (by only the retina visual cycle), or with exogenous retinoid after dissociation from the retina. Spectral sensitivity was determined with single-cell suction recordings. The resulting action spectra were used to determine the chromophore content in each cell type based on the absorption spectra of 9-cis and 11-cis pigments.
The spectral sensitivity of salamander cones dark adapted in the isolated retina was similar to that of cones dark-adapted in the intact eye and could be fit by pure A1/A2 11-cis spectral templates without 9-cis contribution. Similar results in mouse also revealed the absence of 9-cis chromophore in cones after regeneration of their pigment by the retina visual cycle. Thus, Müller cells provide cones exclusively with 11-cis chromophore. Despite sharing the same pigment, salamander blue cones, but not green rods, recovered their sensitivity in the isolated retina, suggesting that access to the retina visual cycle is pigment-independent and cone-specific. Consistent with this notion, exogenous 9-cis retinol produced robust sensitivity recovery in bleached red and blue cones but not in red and green rods. Cone dark adaptation was substantially faster when exposing the outer vs the inner segment to 9-cis retinol, suggesting that cis-retinol oxidation occurs in the outer segment.
Müller cells in the retina visual cycle provide cones exclusively with 11-cis chromophore. However, cone outer segments can oxidize 9-cis retinol to 9-cis retinal and use it for pigment regeneration. Thus, commercially available 9-cis retinol is an excellent alternative to the unstable 11-cis retinol for studying the retina visual cycle.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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