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Rikard Frederiksen, Ala Morshedian, Alapakkam P Sampath, Gordon L Fain; Rod photoresponse recovery and pigment regeneration in bright, persistent light. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4241.
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© ARVO (1962-2015); The Authors (2016-present)
Of the two photoreceptor types in the vertebrate retina, cones are traditionally thought to be functional in bright (photopic) light intensities and rods are mainly responsible for scotopic (dim light) vision. The high sensitivity of rods has led to the notion that they saturate when exposed to moderate light intensities, and thus contribute little to vision in bright light. However, recent studies have challenged this view and suggest that during prolonged illumination rods emerge from saturation and respond to flashes during the presentation of bright background light. We tested this idea with photoreceptor recordings from whole, isolated Gnat2cpfl3/cpfl3 mouse retinas.
Isolated light responses from were recorded with ex vivo trans-retinal ERG from Gnat2cpfl3/cpfl3 retinas in the presence of steady, bright background light. We quantified the amount of pigment bleaching during the exposure to background light, using cellular microspectrophotometry (MSP) to measure spectral absorbance. An analytical model was developed and fitted to the data.
During prolonged exposure to bright light (100,000 – 1,000,000 effective Rh*/s) rods recovered responsiveness from initial saturation and increased their response amplitude over time. Furthermore, the rate of response recovery increased with increasing light intensity. Interestingly, rods remained responsive even after light exposures that bleached nearly all the rhodopsin. Our MSP data suggest that a light-dependent pigment regeneration mechanism counteracts pigment bleaching to maintain a very low level of rhodopsin which supports rod responsiveness in bright, persistent light. Moreover, dark-adapted mouse rods appeared to maintain a pool of chromophore in darkness that regenerates up to ~ 8.5% of the visual pigment.
Rods can emerge from saturation in bright, steady light. We propose that this responsiveness is sustained by a light-dependent pigment regeneration mechanism perhaps within the rods themselves. Maintaining some dynamic range may support rod contributions to vision in bright light as well as help to prevent photoreceptor degeneration in continuous illumination.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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