| A "single cell" approach was applied to the study of visual pigment bleaching in rod photoreceptors. After intact toad eyes were exposed to light, rod photoreceptors were removed and studied microspectrophotometrically. Under "bleaching only" conditions, the axial gradients of rhodopsin remaining were observed to change, as a function of the number of rhodopsins bleached, and the wavelength of the illuminant. These gradients showed good agreement to a proposed model. The derivation of this model was based upon some of the known properties of visual pigments and their arrangement within the rod outer segment.;Physiological mechanisms for pigment regeneration exist in vertebrate eyes. Rhodopsin distributions were studied in toads illuminated for long periods of time, where bleaching and regeneration were allowed to occur together. Using either dim white light or dim 500 nm light, the axial distributions observed in the rods still conformed to the "bleaching only" model, even after exposures lasting up to 2 hours. But after 4 hours, a redistribution occurred. The rhodopsin content became highest in the region where the "bleaching only" model predicted that it should be the lowest.;When the monochromatic illuminant was attenuated tenfold, the gradient reversal was not observed. The axial patterns of rhodopsin remaining could be described by the "bleaching only" model after light exposure periods lasting up to 4 hours.;The distributions of rhodopsin remaining provide some understanding of the patterns of excitation and adaptation in rod photoreceptors. Some of the possible consequences to vision are discussed.;Extremely bright, brief flashes of white light are known to cause photoreversal in the eyes of living animals. Using this kind of light, the intracellular distributions of rhodopsin remaining in the rod outer segments were shown to resemble those obtained after nonphotoreversing illumination. Subtle differences were detectable, though. |
