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Rikard Frederiksen, Soile Nymark, Justin D. Berry, Alexander V. Kolesnikov, Vladimir J. Kefalov, M Carter Cornwall; The Role of Meta III in Regulating Visual Pigment Regeneration and Sensitivity Recovery in Bleached Mouse Rods. Invest. Ophthalmol. Vis. Sci. 2012;53(14):740.
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The purpose of our study was to examine the role of Meta III, a long-lived product of rhodopsin bleaching, in regulating the rate of pigment regeneration and sensitivity recovery in mouse rods. We did this by varying the decay rate of Meta III in intact rod outer segments, and then determined the effects of this change on pigment regeneration rate and sensitivity recovery.
We used microspectrophotometry to measure the rates of Meta III production and decay following bleaching. Subsequently, we measured the rate of visual pigment regeneration after exogenous treatment with 11-cis retinal. These data were correlated with the time course of the recovery of rod sensitivity by suction-electrode recordings from single cells. The experiments were performed in retinae of wild-type mice, as well as those of arrestin-/- and GRK1-/- mice. All measurements were made at 37oC.
We observed the following: (1) In wild-type retinae exposed to light that bleached >90% of the rod visual pigment, Meta III concentration rises to a peak in ~6 min and declines with a time constant of ~18 min. (2) The time course of Meta III decay can be slowed or accelerated by post-bleach exposure to 390 nm or 460 nm light, respectively. (3) Meta III decay is remarkably slowed in bleached arrestin-/- rod outer segments, having a time constant of ~44 min. (4) In GRK1-/- rod outer segemts, MIII decay is instead accelerated (time constant: ~12 min). (5) After Meta III had been allowed to completely decay, exogenous treatment with 11-cis retinal resulted in complete pigment regeneration over the next 30 min whereas sensitivity recovery required a significantly longer time.
Our results indicate that post-bleach exposure to light or the deletion of arrestin can dramatically affect Meta III production and decay. Such regulation of Meta III will be useful for understanding its role in modulating rod dark adaptation.
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