Hara T, Hara R
J Gen Physiol. 1976 Jun;67(6):791-805. doi: 10.1085/jgp.67.6.791.
The cephalopod retina contains two kinds of photopigments, rhodopsin and retinochrome. For many years retinochrome has been thought to be localized in the inner segments of the visual cells, whereas rhodopsin is in the outer segments. However, it is now clear that retinochrome can be extracted also from fragments of outer segments. In the dark-adapted retina of Loligo pealei retinochrome is distributed half-and-half in the inner and outer segments. Todarodes pacificus contains much more retinochrome than Loligo, and it is more abundant in the outer than in the inner segments. The outer segments of Loligo contain retinochrome and metarhodopsin in addition to rhodopsin, whether squids are kept in the dark or in the light. But there is extremely little metarhodopsin (about 3% of rhodopsin) even in light-adapted eyes. The inner segments contain only retinochrome, and much less in the light than in the dark. On the other hand, retinochrome in the outer segments increases markedly during light adaptation. These facts suggest the possibility that some retinochrome moves forward from the inner to the outer segments during light adaptation and there reacts with metarhodopsin to promote regeneration of rhodopsin.
头足类动物的视网膜含有两种光色素，视紫红质和视网膜色素。多年来，人们一直认为视网膜色素定位于视觉细胞的内段，而视紫红质则位于外段。然而，现在很清楚，视网膜色素也可以从外段碎片中提取出来。在暗适应的佩氏枪乌贼视网膜中，视网膜色素在内段和外段中各占一半。太平洋褶柔鱼含有的视网膜色素比枪乌贼多得多，并且在外段比在内段更为丰富。无论乌贼是处于黑暗还是光照环境中，枪乌贼的外段除了视紫红质外还含有视网膜色素和变视紫红质。但是，即使在光适应的眼睛中，变视紫红质的含量也极少（约为视紫红质的3%）。内段仅含有视网膜色素，且在光照下比在黑暗中含量少得多。另一方面，外段中的视网膜色素在光适应过程中显著增加。这些事实表明，在光适应过程中，一些视网膜色素可能从内段向前移动到外段，并在那里与变视紫红质反应以促进视紫红质的再生。
