Kinetics of Rhodopsin’s Chromophore Monitored in a Single Photoreceptor

Abstract

Absorption of light isomerizes the retinyl chromophore of the photoreceptor pigment rhodopsin from 11-cis to all-trans, generating the photoactivated rhodopsin form. The photoisomerization of the chromophore however destroys rhodopsin, and its regeneration requires the removal of the all-trans and the supply of fresh 11-cis chromophore. The all-trans chromophore is removed through a series of steps beginning with its release from photoactivated rhodopsin in the form of all-trans-retinal, leaving behind the apoprotein opsin. All-trans-retinal is then reduced to all-trans-retinol, which is transported out of the photoreceptor. Rhodopsin is regenerated from opsin and fresh 11-cis-retinal arriving to the photoreceptor from the retinal pigment epithelium. Both all-trans and 11-cis-retinal can form precursors of lipofuscin, a pigment that accumulates with age in the lysosomal compartment of the retinal pigment epithelium. All-trans-retinal, all-trans-retinol, and lipofuscin precursors all emit significant and distinct fluorescence signals, allowing their monitoring in single photoreceptor cells with fluorescence imaging. Here we describe the procedures for measuring these fluorophores in single mouse rod photoreceptors.

Interphotoreceptor retinoid–binding protein removes all-trans-retinol and retinal from rod outer segments, preventing lipofuscin precursor formation

“…The levels of all-trans-retinol, all-trans-retinal, and lipofuscin precursors can be measured in single rod photoreceptors by imaging their fluorescence (29). The removal of all-trans-retinol by IRBP has been previously characterized with single cell fluorescence imaging in the large photoreceptor cells from amphibian retinas (30).…”

The First Steps of the Visual Cycle in Human Rod and Cone Photoreceptors

“…The levels of all- trans retinol and all- trans retinal can be measured with high resolution in real time in single photoreceptor cells by imaging their fluorescence. 21 Here, we report on the characterization of the kinetics of all- trans retinol formation in single rod and cone photoreceptor cells isolated from human donor eyes ( Fig. 1 ) with fluorescence imaging.…”