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H.R. Matthews, M.C. Cornwall, R.K. Crouch; Enhancement by 11-cis-9-demethylretinal of Changes in Rod Dim Flash Response Kinetics During Light Adaptation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2002.
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Purpose: During light adaptation Ca2+ acts on a step early in phototransduction that takes place with a time constant of ~0.5 s (Matthews (1997) J. Gen. Physiol. 109, 141). In rods that have been bleached and regenerated with 11-cis-9-demethylretinal, which forms a photopigment with a prolonged photoactivated lifetime (Corson et al. (1994), Vis. Neurosci. 11, 91), the time course of Ca2+-dependent photopigment quenching is greatly prolonged so that it dominates the recovery of the bright flash response (Matthews et al. (2001), J. Gen. Physiol. 118, 377). In order to investigate the shaping of the dim flash response, we have studied dim flash response kinetics during light adaptation in rods containing the 9-demethylretinal pigment. Methods: Isolated salamander rods were exposed to intense 500 nm light calculated to bleach >99% of the photopigment, and regenerated by exposure to phospholipid vesicles containing 9-demethlyretinal. Results: In a bleached rod regenerated with 9-demethlyretinal, the response in darkness to a 440 nm dim flash, which preferentially excites the analogue photopigment, was substantially prolonged in comparison with the response to a 650 nm flash, which preferentially excites remaining native pigment. Steady 610 nm light of increasing intensity progressively accelerated the flash response in a graded manner at both wavelengths, but had a much more profound effect on the recovery kinetics of the response to the 440 nm flash than that to the 650 nm flash. Near-saturating steady light accelerated the time for 50% recovery of the response to the 440 nm flash from 8.3 ± 0.5 to 3.5 ± 0.3 s (means ± SEM, 9 cells), and the response to the 650 nm flash from 2.1 ± 0.1 to 0.89 ± 0.09 s; the light-induced decrease in response duration was significantly different at the two wavelengths. In contrast, the effect of background light on the rising phase of the normalized response differed little at the two wavelengths. Conclusions: When the 9-demethylretinal pigment is stimulated with a dim 440 nm flash the recovery phase of the response is dominated by the greatly-slowed Ca2+-sensitive quenching of the analogue photopigment, thereby enhancing the modulation of response recovery as [Ca2+]i falls during background light.
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