Photoreceptor autophagy: Effects of light history on number and opsin content of degradative vacuoles

PURPOSE. TO investigate whether regulation of rhodopsin levels as a respons e to changed lighting environment is performed by autophagic degradation of opsin in rod inner segments (RISs). METHODS. Groups of albino rats were kept in 3 lux or 200 lux. At 10 weeks o f age, one group was transferred from 3 lux to 200 lux, another group was s witched from 200 lux to 3 lux, and two groups remained in their native ligh ting (baselines). Rats were killed at days 1, 2, and 3 after switching. Ano ther group was switched from 3 lux to 200 lux, and rats were killed at shor t intervals after the switch. Numbers of autophagic vacuoles (AVs) in RISs mere counted, and immunogold labeling was performed for opsin and ubiquitin in electron microscopic sections. RESULTS. The number of AVs increased significantly after switching from 3 l ux to 200 lux at days 1 and 2 and declined at day 3, whereas the reverse in tensity change did not cause any increase, Early time points after change f rom 3 lux to 200 lux showed a significant increase of AVs 2 and 3 hours aft er smirching. Distinct opsin label was observed in AVs of rats switched to 200 lux. Ubiquitin label was present in all investigated specimens and was also seen in AVs especially in 200-lux immigrants. CONCLUSIONS. Earlier studies had shown that an adjustment to new lighting e nvironment is performed by changes in rhodopsin levels in ROSs. Autophagic degradation of opsin or rhodopsin may subserve, at least in part, the adapt ation to abruptly increased habitat illuminance by removing surplus visual pigment.