April 2010
Volume 51, Issue 13
ARVO Annual Meeting Abstract  |   April 2010
Oxidase Activity in the Nrl-/-Rpe65-/- Mouse Retina: IRBP Improves 11-cis Retinal Production From 11-cis Retinol
Author Affiliations & Notes
  • R. O. Parker
    Medical Univ of South Carolina, Charleston, South Carolina
  • R. K. Crouch
    Medical Univ of South Carolina, Charleston, South Carolina
  • Footnotes
    Commercial Relationships  R.O. Parker, None; R.K. Crouch, None.
  • Footnotes
    Support  NIH EY004939 and RPB Senior Scholars Award (RKC), and RPB Medical Student Award (ROP).
Investigative Ophthalmology & Visual Science April 2010, Vol.51, 4810. doi:
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      R. O. Parker, R. K. Crouch; Oxidase Activity in the Nrl-/-Rpe65-/- Mouse Retina: IRBP Improves 11-cis Retinal Production From 11-cis Retinol. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4810.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : An intra-retinal visual cycle is thought to provide cones with a privileged source of chromophore by isomerizing all-trans retinol to 11-cis retinol in Muller cells. To complete the cycle, 11-cis retinol must enter the cone inner segment, where an oxidation reaction regenerates 11-cis retinal. Characterizing the isomerization and oxidation steps of the cone visual cycle in rod-dominant retinae is complicated by the paucity of cones and the activity of the classical visual cycle. The use of Nrl-/-Rpe65-/- mice, which lack both rods and a classical visual cycle, may provide an alternative approach to studying the mammalian cone visual cycle. The goal of our current work is to identify and characterize the oxidase and isomerase reactions of the cone visual cycle using Nrl-/-Rpe65-/- mice.

Methods: : Retina explants in mammalian Ringer’s (37oC) were used to test for oxidase activity in Nrl-/-Rpe65-/- mice (P15). Explants were treated with 11-cis retinol (20uM; 24uM BSA or 24uM IRBP) and 11-cis retinal production was followed by HPLC. To probe for the presence of a second isomerase, Nrl-/-Rpe65-/- mice (P15) were treated with all-trans retinol (0.5 mg, i.p) and UV ERGs were analyzed.

Results: : The presence of oxidase activity was shown by the generation of 11-cis retinal from explants treated with 11-cis retinol. BSA was an adequate vehicle for 11-cis retinol delivery, but IRBP produced 3.5 fold more 11-cis retinal (7.5 vs. 2.2 pmol/retina). The presence of a second isomerase was suggested by improved UV ERGs after treatment with all-trans retinol. Responses to UV stimuli were significantly larger than vehicle and control groups.

Conclusions: : Retina explants from Nrl-/-Rpe65-/- mice show significant levels of oxidase activity. The increased oxidase activity with IRBP suggests a physiological role for IRBP in the delivery of 11-cis retinol to cones in the cone visual cycle. Improved UV ERGs in Nrl-/-Rpe65-/- mice treated with all-trans retinol suggests that isomerase activity may exist in the absence of RPE65.

Keywords: photoreceptors • retinoids/retinoid binding proteins • Muller cells 

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