Wang Jin-Shan, Estevez Maureen E, Cornwall M Carter, Kefalov Vladimir J
Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, 660 South Euclid Ave., Saint Louis, Missouri 63110, USA.
Nat Neurosci. 2009 Mar;12(3):295-302. doi: 10.1038/nn.2258. Epub 2009 Feb 1.
Daytime vision is mediated by retinal cones, which, unlike rods, remain functional even in bright light and dark-adapt rapidly. These cone properties are enabled by rapid regeneration of their pigment. This in turn requires rapid chromophore recycling that may not be achieved by the canonical retinal pigment epithelium visual cycle. Recent biochemical studies have suggested the presence of a second, cone-specific visual cycle, although its physiological function remains to be established. We found that the Müller cells in the salamander neural retina promote cone-specific pigment regeneration and dark adaptation that are independent of the pigment epithelium. Without this pathway, dark adaptation of cones was slow and incomplete. Notably, the rates of cone pigment regeneration by the retina and pigment epithelium visual cycles were essentially identical, suggesting a possible common rate-limiting step. Finally, we also observed cone dark adaptation in the isolated mouse retina.
白天的视觉由视网膜视锥细胞介导，与视杆细胞不同，视锥细胞即使在强光下也能保持功能，并且能迅速适应暗环境。这些视锥细胞的特性是由其色素的快速再生实现的。这反过来又需要快速的发色团循环利用，而经典的视网膜色素上皮视觉循环可能无法实现这一点。最近的生化研究表明存在第二种视锥细胞特异性视觉循环，尽管其生理功能仍有待确定。我们发现，蝾螈神经视网膜中的米勒细胞促进了视锥细胞特异性色素再生和暗适应，且这一过程独立于色素上皮。没有这条途径，视锥细胞的暗适应就会缓慢且不完全。值得注意的是，视网膜和色素上皮视觉循环对视锥细胞色素再生的速率基本相同，这表明可能存在一个共同的限速步骤。最后，我们在分离的小鼠视网膜中也观察到了视锥细胞的暗适应。
