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Rikard Frederiksen, Soile Nymark, Justin Berry, Alexander V Kolesnikov, Vladimir J Kefalov, M Carter Cornwall; Meta III Limits Opsin Availability During Pigment Regeneration in Bleached Mouse Rods. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5959.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose was to determine if Meta III, a product of rhodopsin bleaching, limits the availability of opsin for rhodopsin regeneration in mouse rods. We did this by varying the decay rate of Meta III in intact rod outer segments, and then determined differences in pigment regeneration rate.
Experiments were performed in isolated intact retinae of WT, Arr1-/-, and Grk1-/- mice. We used microspectrophotometry to measure the rates of Meta III production and decay following bleaching. Subsequently, we measured the amount of rhodopsin regenerated after exogenous treatment with 11-cis retinal at different stages of Meta III decay.
In WT retinae exposed to light that bleached >90% of rhodopsin, Meta III concentration rose to a peak in ~6 min and decayed with a time constant of ~18 min. This time course could be slowed by post-bleach exposure to 390 nm light, producing a stable Meta III like photoproduct. Similarly, Meta III decay was remarkably slowed in bleached Arr1-/- rod outer segments, with a correspondent decay time constant of ~44 min. In contrast, Meta III decay in bleached Grk1-/- rod outer segments was accelerated (time constant: ~12 min). When treated exogenously with 11-cis retinal at different stages of Meta III decay, the amount of pigment regenerated in these three models was consistent with their rates of Meta III decay. Rhodopsin regeneration was most rapid in Grk1-/- rod outer segments compared to WT, but much slower in Arr1-/- rod outer segments. However, once Meta III had decayed fully, treatment with exogenous 11-cis retinal resulted in complete pigment regeneration in all models.
Our data demonstrate that post-bleach exposure to bright UV light or the deletion of Arr1 or Grk1 can dramatically alter the time course of Meta III production and decay. The presence of Meta III prevents the regeneration of rhodopsin whose rate could be regulated by these two proteins in vivo.
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