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Ambarish S. Pawar, Nasser M. Qtaishat, Deborah M. Little, David R. Pepperberg; Recovery of Rod Photoresponses in ABCR-Deficient Mice. Invest. Ophthalmol. Vis. Sci. 2008;49(6):2743-2755. doi: 10.1167/iovs.07-1499.
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purpose. The ABCR protein of the rod outer segment is thought to facilitate movement of the all-trans retinal photoproduct of rhodopsin bleaching out of the disc lumen. This study was undertaken to investigate the extent to which ABCR deficiency affects the post-bleach recovery of the rod photoresponse in ABCR-deficient (abcr − / −) mice.
methods. Electroretinographic (ERG) a-wave responses were recorded from abcr − / − mice and two control strains. A bright probe flash was used to examine the course of rod recovery after fractional rhodopsin bleaches of ∼10−6, ∼3 × 10−5, ∼0.03, and ∼0.30 to ∼0.40.
results. Dark-adapted abcr − / − mice and control animals exhibited similar normalized near-peak amplitudes of the paired-flash-ERG-derived, weak-flash response. Response recovery after ∼10−6 bleaching exhibited an average exponential time constant of 319, 171, and 213 ms, respectively, in the abcr − / − and the two control strains. Recovery time constants determined for ∼3 × 10−5 bleaching did not differ significantly among strains. However, those determined for the ∼0.03 bleach indicated significantly faster recovery in abcr − / − mice (2.34 ± 0.74 minutes) than in the controls (5.36 ± 2.20 and 5.92 ± 2.44 minutes). After ∼0.30 to ∼0.40 bleaching, the initial recovery in the abcr − / − mice was, on average, faster than in control mice.
conclusions. By comparison with control animals, abcr − / − mice exhibit faster rod recovery after a bleach of ∼0.03. The data suggest that ABCR in normal rods may directly or indirectly prolong all-trans retinal clearance from the disc lumen over a significant bleaching range, and that the essential function of ABCR may be to promote the clearance of residual amounts of all-trans retinal that remain in the discs long after bleaching.
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