THE REGENERATION OF RHODOPSIN AFTER SMALL BLEACHES IN THE ISOLATED AMPHIBIAN RETINA (RETINOIDS, METABOLISM, VISUAL CYCLE)
Abstract
The capacity of the isolated perfused frog R. catesbeiana and toad B. marinus retina to regenerated rhodopsin after a series of low level bleaches (('-)2% - 5%) was investigated. The absorbance of the retina was monitored in a way which permitted an accurate determination of small changes in the concentration of rhodopsin. Each retina received a 2 min. light exposure that bleached a small fraction of the rhodopsin. The absorbance of the retina decreased immediately after the bleach and then began to increase with time reaching its maximal level in approximately 60 minutes (T = 25(DEGREES)C). Additional bleaches were then performed. Complete regeneration of the bleached rhodopsin was observed only after the first bleach with less or no regeneration occurring after subsequent bleaches. The average total regeneration in both the frog and toad was approximately 3% of the rhodopsin present. This agrees well with the size of 11-cis retinol stores in the amphibian retina. Thus, the amount of regeneration of visual pigment may be explained on the basis of the utilization of chromophoric stores. The effect of the magnitude of the bleach on the regeneration of rhodopsin was also investigated. As the fraction of rhodopsin bleached increased the regenerative capacity of the retina declined. This suggests that light may play a regulatory role in the process of regeneration, perhaps by altering the metabolism of the photoreceptor cell. The effects of altering the cGMP of the photoreceptor cell within physiological limits, as well as the exogenous addition of cGMP on the regeneration of rhodopsin were also investigated. Finally, the regenerative potential of the retina was followed when a limited degree of contact with the pigment epithelium was maintained or when the isolated retina was incubated in the presence of the enzyme alcohol dehydrogenase. From the results obtained it appears that the isolated amphibian retina can utilize its store of 11-cis retinol for the regeneration of a small fraction of its rhodopsin and the ability to utilize the pool of 11-cis retinol appears to depend on the metabolic state of the photoreceptor cell.
Degree
Ph.D.
Subject Area
Neurology
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