Recovery of rod photoresponses in ABCR-deficient mice.
OBJECTIVE
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 approximately 10(-6), approximately 3 x 10(-5), approximately 0.03, and approximately 0.30 to approximately 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 approximately 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 approximately 3 x 10(-5) bleaching did not differ significantly among strains. However, those determined for the approximately 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 approximately 0.30 to approximately 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 approximately 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.
Pawar
Ambarish S
AS
Lions of Illinois Eye Research Institute, Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois. 60612, USA.
Qtaishat
Nasser M
NM
Little
Deborah M
DM
Pepperberg
David R
DR
D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000818:Animals; D003623:Dark Adaptation / Q000502:physiology; D004596:Electroretinography; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010775:Photic Stimulation; D020127:Recovery of Function; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology* / Q000528:radiation effects; D012243:Rhodopsin / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology*
D018528:ATP-Binding Cassette Transporters; C512841:Abca4 protein, mouse; D012243:Rhodopsin