This research project addresses a central issue in the cell biology of vision and photoreception: the mechanisms and significance of turnover of light- sensitive membrane and its constituent light-sensitive molecule (rhodopsin). The assembly of light-sensitive membranes in light receptors are being studied in the normal and also in the vitamin-A deprived condition. Intracellular membranes that serve as the precursors of photosensitive membranes accumulate as large masses within vitamin-A deficient photoreceptors. When such cells are exposed to very bright light that compensates for their relative insensitivity, the internal membrane is rapidly added to the light-sensitive membrane. This laboratory also is testing an hypothesis concerning the relationship between the biochemical pathway that is involved in the response to light and the regulation of assembly and degradation of the light-sensitive membrane in photoreceptors. Techniques being used include pharmacological agents that specifically mimic various steps in the biochemical pathway. The structural effects of these agents on photoreceptor cells will be studied with electron microscopy. Functional effects will be assessed with electrophysiological methods. The pathway by which vitamin A derivatives enter and are utilized by the retina to provide the light-sensitive molecules for photoreception is also being investigated.
