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A.D. Marmorstein, J. Yocom, B. Stanton, B. Bakall, P.J. McLaughlin, M.T. Schiavone, C. Wadelius, L.Y. Marmorstein, N.S. Peachey; Effects of Overexpression of Bestrophin and Best Macular Dystrophy Associated Mutants of Bestrophin on the Rat DC-ERG . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5101.
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Purpose: To determine the effects of wild type and mutant bestrophin overexpression on the light peak of the rat DC-ERG. Methods: Adenovirus-mediated gene transfer was used to express wild type bestrophin (wt-best), or two bestrophin mutants (W93C, R218C) associated with Best macular dystrophy (BMD) in the RPE of adult Long-Evans rats. Two weeks after subretinal injection, the retina and RPE were analyzed by fundus exam, conventional and DC-ERG recordings, histology, and immunofluorescence. Results: Using doses between 0.2 x 107 and 5 x 107 pfu, wt-best and both the W93C and R218C mutants correctly localized to the basolateral plasma membrane of the RPE. No defects were noted on fundus exams and the morphology of the retina, RPE, and choroid was typically preserved. While an effect of viral load was noted on conventional ERG amplitudes, these effects did not differ from a null virus control. DC-ERGs recorded in response to a 5-min flash stimulus displayed consistent changes in the light peak (LP) when compared against sham- or null virus-injected controls. While LP amplitude did not change in eyes overexpressing wt-best, the LP time constant (τ) was significantly accelerated. In eyes overexpressing W93C or R218C, LP amplitude was significantly lowered vs. null controls. In addition, τ was significantly slowed in W93C animals but unaltered in animals receiving R218C. In normal, control, or wt-best rats, LP onset occurred ~112 sec after stimulus presentation. In eyes receiving R218C, LP onset was delayed, to 130-135 sec. No defects in LP sensitivity were noted, although the LP continued to increase with longer stimulus durations in W93C transduced eyes only. Conclusions: Overexpression of wt-best accelerates the LP kinetics, but does not affect LP amplitude or the other components of the DC-ERG. BMD associated mutants exhibit LP reductions and delays that mimic the electrooculographic abnormalities seen in BMD patients. Differences between the effects induced by W93C and R218C suggest a complex mechanism behind bestrophin activity.
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