Molina T M, Torres S C, Flores A, Hara T, Hara R, Robles L J
Department of Biology, California State University, Carson 90747.
Exp Eye Res. 1992 Jan;54(1):83-90. doi: 10.1016/0014-4835(92)90072-z.
The cephalopod retina contains two photopigments that are spatially separated within the photoreceptors; rhodopsin, localized in the light-sensitive rhabdoms, and retinochrome, present in the myeloid bodies of the photoreceptor inner segments. In the light, the chromophore of retinochrome, all-trans retinal, is photoisomerized to 11-cis to form metaretinochrome. Metaretinochrome is believed to serve as a store for 11-cis retinal used in the regeneration or biosynthesis of rhodopsin. Previous studies suggest that a soluble retinal binding protein (RALBP) serves as a shuttle between retinochrome and rhodopsin, and, in the dark, may transport chromophore from the myeloid bodies to the rhabdoms. Our study supports this hypothesis and demonstrates that RALBP is in the correct cellular locations to function as a shuttle. Dark- and light-adapted octopus retinas were labeled with anti-RALBP using immunofluorescence and immunogold techniques. Our results showed that RALBP was distributed differently in the dark- and light-adapted retinas. Our most significant observation was that myeloid bodies from light-adapted retinas were more heavily labeled by anti-RALBP than myeloid bodies in dark-adapted retinas. The rhabdomeres, interphotoreceptor matrix, and inner limiting membrane were also labeled in both light and dark conditions. Based on these results and evidence from previous biochemical studies, we conclude that in the dark RALBP leaves the myeloid bodies and transports 11-cis retinal to the rhabdoms where chromophore exchange with metarhodopsin may occur.
头足类动物的视网膜含有两种光色素，它们在光感受器内呈空间分离状态；视紫红质位于对光敏感的视小杆中，而视黄醛色素存在于光感受器内段的髓样体中。在光照下，视黄醛色素的发色团全反式视黄醛被光异构化为11-顺式视黄醛，形成变视黄醛色素。变视黄醛色素被认为是视紫红质再生或生物合成中使用的11-顺式视黄醛的储存库。先前的研究表明，一种可溶性视黄醛结合蛋白（RALBP）在视黄醛色素和视紫红质之间起穿梭作用，并且在黑暗中可能将发色团从髓样体转运到视小杆。我们的研究支持这一假设，并证明RALBP在正确的细胞位置发挥穿梭作用。使用免疫荧光和免疫金技术，用抗RALBP对暗适应和明适应的章鱼视网膜进行标记。我们的结果表明，RALBP在暗适应和明适应的视网膜中的分布不同。我们最显著的观察结果是，明适应视网膜的髓样体比暗适应视网膜的髓样体被抗RALBP标记得更强烈。在明、暗条件下，视小杆、光感受器间基质和内界膜也都被标记。基于这些结果以及先前生化研究的证据，我们得出结论，在黑暗中，RALBP离开髓样体，将11-顺式视黄醛转运到视小杆，在那里可能发生发色团与变视紫红质的交换。
