Recovery of rod photoresponses in ABCR-deficient mice

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 similar to 10(-6), similar to 3 x 10(-5), similar to 0.03, and similar to 0.30 to similar 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 similar to 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 similar to 3 x 10(-5) bleaching did not differ significantly among strains. However, those determined for the similar to 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 similar to 0.30 to similar 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 similar to 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.