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Rikard Frederiksen, Rosalie K. Crouch, Benjamin Nickle, Kaylan S. Chakrabarti, Carter Cornwall; Regulation of the Rate of Pigment Regeneration and its Relationship to Dark Adaptation and Recovery of Sensitivity in Vertebrate Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1179.
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Native visual pigments in vertebrate and invertebrate photoreceptors use retinal-based chromophores that are linked to opsins. 11-cis Retinal and 11-cis 3,4 dehydro retinal are found principally in vertebrate rods and cones, but also in many invertebrate eyes. In addition to these, certain invertebrate eyes also use 11-cis 4-OH retinal and 11-cis 3-OH retinal as chromophores. We have performed experiments to determine the mechanism that underlies the much more rapid pigment regeneration and dark-adaptation that are observed in vertebrate photoreceptors when their visual pigment is regenerated to contain 11-cis 4-OH rhodopsin.
Microspectrophotometric measurements of visual pigment content and single cell measurements of receptor sensitivity were made on salamander photoreceptors in darkness prior to light exposure, in subsequent darkness after >99% of the pigment had been bleached, and at different times during pigment regeneration. Two different retinoids were exogenously applied to bleached rods to promote visual pigment regeneration - 11-cis retinal (A1) and 11-cis 4-hydroxy retinal (A4).
After treatment with A1 or A4, bleached salamander photoreceptors form functional pigment. Sensitivity, dark current and kinetics recover fully to dark-adapted levels. However, rods and cones treated with A4 exhibited roughly 5-fold acceleration in pigment formation and recovery of sensitivity compared to bleached cells treated with A1. This occurs in spite of the fact that expressed bovine rod opsin purified from HEK 293S cells treated with A4 regenerates visual pigment about 4-fold slower than that regenerated with A1.
Our results are consistent with the notion that the more rapid photopigment regeneration and dark adaptation that we observe in rods and cones treated with 11-cis 4OH retinal results from its more efficient access to the opsin, perhaps due to its greater aqueous solubility compared to 11-cis retinal.
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