Recovery of rod photoresponses in ABCR-deficient mice
Ambarish S. Pawar 1,
Nasser Qtaishat 2,
Deborah M Little 3,
and
David R. Pepperberg 4*
1 Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States; Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States
2 Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States
3 Neurology & Rehabilitation, University of Illinois at Chicago, Chicago, Illinois, United States
4 Department of Ophthalmology & Visual Science, University of Illinois at Chicago, Chicago, Illinois, United States
* To whom correspondence should be addressed. E-mail: davipepp{at}uic.edu.
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Abstract |
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Purpose: ABCR protein in the rod outer segment is thought to facilitate movement of the all-trans retinal photoproduct of rhodopsin bleaching out of the disk lumen. We investigated the extent to which ABCR deficiency affects 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. Using a bright probe flash, we examined the course of rod recovery following fractional rhodopsin bleaches of ~10-6, ~3x10-5, ~0.03 and ~0.30-0.40. Results: Dark-adapted abcr-/- mice and controls exhibited similar normalized near-peak amplitudes of the paired-flash-ERG-derived, weak-flash response. Response recovery following ~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 ~3x10-5 bleaching did not differ significantly among strains. However, those determined for the ~0.03 bleach indicated significantly faster recovery in abcr-/- (2.34 + 0.74 min) than in the controls (5.36 + 2.20 min, and 5.92 + 2.44 min). Following ~0.30-0.40 bleaching, the initial recovery in the abcr-/- was on average faster than in controls. Conclusions: By comparison with controls, abcr-/- mice exhibit faster rod recovery following a bleach of ~0.03. The data suggest that ABCR in normal rods may directly or indirectly prolong all-trans retinal clearance from the disk 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 disks long after bleaching.
Key Words:
rods, dark adaptation, electroretinography, ABCR, ABCA4
