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B-A. Battelle, A Parker, C. Gaddie, K. Kempler; Long-term Dark Adaptive Biochemistry Of Photoreceptors Is Influenced By Time Of Day. Invest. Ophthalmol. Vis. Sci. 2011;52(14):916.
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To test whether the long-term dark-adaptive biochemistry of photoreceptors is influenced by time of day.
Opsin1-2 (Ops1-2) and arrestin (Arr) levels associated with the photosensitive rhabdomeres of Limulus lateral eye photoreceptors (RhOps1-2, RhArr) were quantified with immunocytochemistry (ICC) and confocal microscopy. Eyes were fixed at different times of the day and under different lighting conditions; then frozen sections were processed for ICC. RhOps1-2 and RhArr were compared: 1. between daytime (DT) light-adapted and nighttime (NT) dark-adapted eyes.2. among eyes taken at different times as animals transitioned from day to night under natural illumination. 3. between DT light-adapted eyes and DT eyes that had been dark-adapted for 4hr.
RhOps1-2 in DT light-adapted eyes was 58% (p< 0.001) below that in NT dark-adapted eyes. RhOps1-2 increased slowly during dusk but was at the maximum NT level by 4hr after sunset (SS). When eyes were dark-adapted for 4hr during the day, RhOps1-2 increased 23% (p=0.001) but was still significantly (35%, p=0.005) below that in NT dark-adapted eyes. RhArr in DT light-adapted eyes was 200% the level (p<0.001) in NT dark-adapted eyes. RhArr fell rapidly at dusk and was within 25% of the NT level by 30min after SS. RhArr was not significantly different between NT dark-adapted eyes and eyes that were dark-adapted for 4h during the day.
RhOps1-2 in DT dark-adapted eyes is significantly lower than in NT dark-adapted eyes. This supports the idea that RhOps1-2 renewal is influenced by circadian clock input to the eye, which is silent during the day and active during the night. Previous studies showed that RhOps1-2 in eyes deprived of NT clock input is 37% below the normal NT levels, about the same level observed here in DT dark-adapted eyes. RhArr was not significantly different between DT and NT dark-adapted eyes; thus the decrease in RhArr in the dark is not influenced by time of day or clock input. However, because of the different effects of time of day on dark-adapted RhOps1-2 and RhArr levels, the dark-adapted ratio of RhArr to RhOps1-2 will be significantly higher during the day compared to during the night. This suggests that the dynamics of the photoresponse in dark adapted eyes is different between day and night.
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