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Originally published In Press as doi:10.1167/iovs.07-1499 on February 8, 2008
 (Investigative Ophthalmology and Visual Science. 2008;49:2743-2755.)
© 2008 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.07-1499
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Recovery of Rod Photoresponses in ABCR-Deficient Mice

Ambarish S. Pawar,1,2 Nasser M. Qtaishat,1 Deborah M. Little,3 and David R. Pepperberg1,2

1From the Lions of Illinois Eye Research Institute, Department of Ophthalmology and Visual Sciences, and the 3Department of Neurology and Rehabilitation, College of Medicine, and the 2Department of Bioengineering, College of Engineering, University of Illinois at Chicago, Chicago, Illinois.

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 x 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 x 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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