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R. Frederiksen, R. K. Crouch, C. L. Makino, M. C. Cornwall; Lingering Phototransduction Noise After Bright Flashes in Salamander Rods Whose Pigment Was Regenerated With 11-cis 4-hydroxy Retinal. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1112. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previously, we have shown that red rods regenerated with11-cis 4-hydroxy retinal (A4), an analog of the 11-cis retinal chromophore, occurring in some species, exhibit transient dark noise following the response to a saturating flash. The purpose of this study is to characterize this noise in order to determine its origin and to find out whether it is produced by activation of normal phototransduction mechanisms.
Single cell suction pipette recordings were made of dark current, sensitivity, dim flash responses and noise from solitary larval tiger salamander red rods. Recordings were made under dark-adapted conditions, following exposure to bright bleaching light, and after regeneration with A4. Spectral absorbance was also measured microspectrophotometrically.
After treatment with A4, bleached salamander red rods fully recovered sensitivity and dark current within 60 minutes with no difference in absolute sensitivity or absorbance at the peak wavelength compared to native cells. However, the spectral peak of the pigment formed with A4 chromophore was blue-shifted by 30 nm compared to the native pigment. We also observed a significantly lower rate of dark events compared to the native dark-adapted rod. But after presenting the rod with a saturating flash, there was a transient increase in noise. The power spectrum of this noise matched that of spontaneous activations of the phototransduction cascade in darkness as well as that elicited by continuous dim light.
The blue-shifted A4 pigment was more stable and produced fewer dark events than the native pigment. However, the noise level was significantly increased shortly after exposure to bright light apparently due to an inefficient shutoff of photoexcited analog pigment. The mechanism for this transient dark noise appears to be governed by regular phototransduction proteins.
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