Physics (Internal)

Early Steps of the Visual Cycle: Production and Clearance of Retinol in Vertebrate Rod and Cone Photorecetors

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:
Light absorption by visual pigments in vertebrate rod and cone photoreceptors leads to the activation of the visual transduction cascade. At the same time it results in the photochemical destruction (bleaching) of the visual pigment leading to the formation of free all-trans retinal and opsin. The very large differential in the rates of recovery of sensitivity of rods and cones following their exposure to bright light results, at least partially, from their widely different rates of photopigment regeneration. The series of reactions responsible for photopigment regeneration is collectively termed the visual cycle. This talk will focus on a comparative examination of initial steps in the visual cycle in rods and cones. Measurements of two types will be discussed. First, microspectrophotometry of isolated photoreceptors will be described by which determinations of visual pigment content in rods and cones are made under dark-adapted and bleach-adapted conditions. This technique allows measurement of the rate of decay of activated forms in isolated cells following light exposure. Second, microfluorometric measurements of differential rates of reduction of all-trans retinal to all-trans retinol will be described in these same cell types. Results will be considered in relation to the normal maintenance of visual sensitivity under the widely varying conditions of ambient light that exist in the normal environment.