title: Influence of UVA light stress on photoreceptor cell metabolism: decreased rates of rhodopsin regeneration and opsin synthesis.
abstract: There is considerable evidence indicating that rhodopsin is the chromophore mediating light damage to the rat retina caused by exposure to mid-visible wavelengths. Retinal damage is, however, more effectively produced by short-wavelength light, and little is known about the initiating events for this damage class. The present study sought to determine the involvement of rhodopsin bleaching in short-wavelength damage by examining rhodopsin levels and opsin synthesis at early time points following acute ultraviolet-A (UVA) exposures of the pigmented rat eye. A gradual decline in rhodopsin to 8% of the level in non-exposed control eyes occurred over a 1 hr exposure to 1500 microW cm-2of UVA light. When animals were placed in darkness following this exposure, rhodopsin had recovered to only 27% of control levels by 2 hr post-exposure indicating a very slow rate of regeneration. For later time points, animals were returned to dim cyclic light and by 2 days following exposure, rhodopsin levels had risen to 57% of control. In contrast, opsin levels at this same time point were unaffected by UVA exposure. Other observations indicating the UVA exposure affected photoreceptor cell metabolism included a 27% decrease in the rate of opsin synthesis between 1 and 2 days following exposure, and a 69% reduction in the rate of rod outer segment disk renewal during the initial 3 days following exposure. These data show that UVA light stress in the retina causes a gradual bleaching of rhodopsin followed by a slow rate of recovery and altered photoreceptor cell metabolism. These results are consistent with the concept that rhodopsin mediates UVA-induced retinal damage and the possible mechanisms by which this might occur are discussed in relation to alternative hypotheses currently in the literature.
authors.affiliation: Cullen Eye Institute, Baylor College of Medicine, Houston, TX, 77030, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Rapp
authors.forename: A J
authors.initials: AJ
authors.lastname: Ghalayini
mesh_terms: D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D011833:Radiation Injuries, Experimental / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D020318:Rats, Long-Evans; D012243:Rhodopsin / Q000378:metabolism / Q000528:radiation effects*; D012374:Rod Cell Outer Segment / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D017299:Rod Opsins / Q000096:biosynthesis / Q000528:radiation effects*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D017299:Rod Opsins; D012243:Rhodopsin