Rhodopsin kinetics in the cat retina.

Abstract

The bleaching and regeneration of rhodopsin in the living cat retina was studied by means of fundus reflectometry. Bleaching was effected by continuous light exposures of 1 rain or 20 min, and the changes in retinal absorbance were measured at 29 wavelengths. For all of the conditions studied (fractional bleaches of from 65 to 100%), the regeneration of rhodopsin to its prebleach levels required >60 rain in darkness. After the l-rain exposures, the difference spectra recorded during the first 10 min of dark adaptation were dominated by photoproduct absorption, and rhodopsin regeneration kinetics were obscured by these intermediate processes. Extending the bleaching duration to 20 min gave the products of photolysis an opportunity to dissipate, and it was possible to follow the regenerative process over its full time-course. It was not possible, however, to fit these data with the simple exponential function predicted by first-order reaction kinetics. Other possible mechanisms were considered and are presented in the text. Nevertheless, the kinetics of regeneration compared favorably with the temporal changes in log sensitivity determined electrophysiologically by other investigators. Based on the bleaching curve for cat rhodopsin, the photosensitivity was determined and found to approximate closely the value obtained for human rhodopsin; i.e., the energy Er required to bleach 1 -e -] of the available rhodopsin was 7.09 log scotopic troland-seconds (corrected for the optics of the cat eye), as compared with ~7.0 in man.

Loss of Retinoschisin (RS1) Cell Surface Protein in Maturing Mouse Rod Photoreceptors Elevates the Luminance Threshold for Light-Driven Translocation of Transducin But Not Arrestin

“…The rate of formation of bleached rhodopsin is the rate of photon capture, and, under steady-state conditions, in which the rate of regeneration is the same as the rate of bleach, the regeneration rate can be used to calculate the rate of photon capture (Penn and Williams, 1986). First-order kinetics have been widely used to describe the regeneration rate of rhodopsin in rats (Tansley, 1931;Dowling, 1963;Penn and Williams, 1986) and mice , although other models have been proposed based on data from humans (Alpern and Krantz, 1981;Lamb and Pugh, 2004), cats (Ripps et al, 1981), and rodents (Lamb and Pugh, 2004). In addition, the kinetics of regeneration may be different under anesthesia (Perlman, 1978;Keller et al, 2001).…”

Foveal dark adaptation, photopigment regeneration, and aging

“…Delta actually underestimates the true double density of the photopigment owing to the probable inclusion of stray light: photons that have not passed through the pigment but were instead reflected from surfaces above or between the photoreceptors (Ripps et al, 1981;van Norren & van der Kraats, 1981;van Blokland & van Norren, 1986;King-Smith, 1973). Because this stray light is not affected by bleaching, the measured relative total change is always less than the total change due to the pigment.…”

Background and bleaching adaptation in luminosity type horizontal cells in the isolated turtle retina.

“…12). Rods and cones in different species seem to obey the relationship described in eqn (9) under most circumstances but they differ in the value of K. Some typical values for K reported in the literature are: 3 for human cones (Rushton, 1966); 19 and 12 338 for human rods (Rushton, 1966;Alpern, 1971); 6 for rat rods (Dowling, 1963); 5 for skate rods (Dowling & Ripps, 1970) and 6 for cat rods (Ripps, Mehaffey & Siegel, 1981). When bright backgrounds, which produced substantial bleaches (more than 99%), were applied, the loss of sensitivity was larger than expected from the log-linear relationship.…”