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Soile Nymark, Rikard Frederiksen, Michael L. Woodruff, Gordon L. Fain, Carter Cornwall; Visual Pigment Regeneration and Sensitivity Recovery in mouse rods. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6578.
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To develop a method to make simultaneous measurements of pigment absorbance and sensitivity from mouse rods, in order to determine mechanisms regulating recovery of sensitivity in bleached photoreceptors and the relationship between products of photopigment bleaching (Meta II and Meta III) on the one hand, and pigment regeneration rate and recovery of sensitivity on the other.
Visual pigment content within outer segments of mouse rods was determined by microspectrophotometry (MSP), and rod sensitivity by suction-electrode recording from single cells attached to retinal patches from which absorbance measurements were made. Spectral absorbance was correlated with flash response kinetics and sensitivity in darkness before and following pigment bleaching, and at different times after exogenous addition of 11-cis retinal in lipid vesicles.
We observed the following: (1) After a substantial bleach (>90%) and treatment with 11-cis retinal, up to 150 min is required for complete pigment regeneration and sensitivity recovery. (2) As pigment regeneration proceeds, flash response kinetics slow to approach dark adapted values. (3) Meta III concentration following bleaching rises to a peak in about 6 min and declines with a time constant of 17 min. (4) Repeated bright bleaches of Meta II result in a reduction of the time constant for Meta III decay to 8.7 min. Such bleaches do not significantly compromise visual pigment regeneration following treatment with exogenous 11-cis retinal. (5) Subsequent studies have correlated the rate of pigment regeneration and sensitivity recovery with the lifetimes of these photoproduct states.
Our experiments demonstrate that visual pigment regeneration in murine rods following bleaching reverses the steady-state desensitization and flash response acceleration due to bleached opsin, as has been previously demonstrated in amphibian rods. We propose a model in which opsin unavailability, due to the existence of long-lived photoproducts, is responsible for the slowness of pigment regeneration and sensitivity recovery in mammalian rods.
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