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Ala Morshedian, Rikard Frederiksen, Alapakkam P Sampath, Joanna J. Kaylor, Gabriel H Travis, Gordon L Fain; LIGHT-DEPENDENT RECOVERY OF SENSITIVITY AFTER BLEACHING BY PHOTOISOMERIZATION OF RGR IN MOUSE CONES. Invest. Ophthalmol. Vis. Sci. 2019;60(9):563.
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© ARVO (1962-2015); The Authors (2016-present)
Cone photoreceptors can recover after bleaching even in isolated retina from pigment regeneration independent of the RPE in the Müller cells. We now show that this recovery is mostly if not entirely produced in mouse by retinal G-protein receptor (RGR), a protein related to rhodopsin that can use light to convert all-trans retinal to 11-cis retinal.
Isolated cone light responses were recorded from whole retina of Gnat1-/- or Gnat1-/-;RGR-/- mice after blocking responses of other retinal cells with 40 mM D,L-2-amino-4-phosphonobutyric acid (AP4) and 2 mM aspartic acid, in the presence of 4 mM lactate and 10mM all-trans retinol in 0.05% bovine serum albumin at 36–38°C. We used test flashes of 565-nm light, to which M cones are greater than 7 orders of magnitude more sensitive than S cones.
During prolonged exposure to light equivalent to 106 pigment molecules bleached per second, cones continue to respond for at least 4 hours, but responses gradually decline presumably from loss of chromophore during perfusion. The rate of decline is much faster in cones lacking RGR or after poisoning Müller cells with 10 mM α-aminoadiptic acid. The rate was also affected by the wavelength of the continuous illumination, indicating an additional role for an N-retinylidene-PE (N-ret-PE) pathway. Gnat1-/- cones recovered sensitivity in darkness after bleaching over several minutes, but recovery was small or absent in Gnat1-/-;RGR-/- mice. Moreover, recovery depended strongly on the rate of bleaching. If light calculated to bleach 90% of the pigment was given in 350 ms, little recovery was observed; whereas the same bleach given over 5 min showed significant recovery even during light exposure.
Our results suggest that recovery of cone sensitivity by the Müller glial-cell pathway is produced predominantly by light-dependent regeneration of chromophore, and that RGR has a critical role in the maintenance of cone sensitivity during exposure to bright light. We believe that the time constant of sensitivity recovery after bleaching is the result of passage of 11-cis retinol from Müller cells to cones and/or conversion of 11-cis retinol to 11-cis retinal. These experiments demonstrate an important role for RGR and light-dependent pigment regeneration in cone vision.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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