Hamann Steffen
Department of Medical Physiology, The Panum Institute, University of Copenhagen, Denmark.
Int Rev Cytol. 2002;215:395-431. doi: 10.1016/s0074-7696(02)15016-9.
The four major sites for ocular water transport, the corneal epithelium and endothelium, the ciliary epithelium, and the retinal pigment epithelium, are reviewed. The cornea has an inherent tendency to swell, which is counteracted by its two surface cell layers, the corneal epithelium and endothelium. The bilayered ciliary epithelium secretes the aqueous humor into the posterior chamber, and the retinal pigment epithelium transports water from the retinal to the choroidal site. For each epithelium, ion transport mechanisms are associated with fluid transport, but the exact molecular coupling sites between ion and water transport remain undefined. In the retinal pigment epithelium, a H+-lactate cotransporter transports water. This protein could be the site of coupling between salt and water in this epithelium. The distribution of aquaporins does not suggest a role for these proteins in a general model for water transport in ocular epithelia. Some water-transporting membranes contain aquaporins, others do not. The ultrastructure is also variable among the cell layers and cannot be fitted into a general model. On the other hand, the direction of cotransport in symporters complies with the direction of fluid transport in both the corneal epi- and endothelium, as well as the ciliary epithelium and retinal pigment epithelium.
本文综述了眼部水运输的四个主要部位，即角膜上皮和内皮、睫状体上皮以及视网膜色素上皮。角膜具有肿胀的内在倾向，但其两个表面细胞层，即角膜上皮和内皮可抵消这种倾向。双层睫状体上皮将房水分泌到后房，而视网膜色素上皮将水从视网膜运输到脉络膜部位。对于每个上皮组织，离子转运机制都与液体运输相关，但离子与水运输之间确切的分子偶联位点仍不明确。在视网膜色素上皮中，一种H⁺-乳酸共转运蛋白可运输水。该蛋白可能是该上皮组织中盐与水偶联的位点。水通道蛋白的分布并不表明这些蛋白在眼部上皮水运输的一般模型中起作用。一些水运输膜含有水通道蛋白，而另一些则没有。细胞层之间的超微结构也各不相同，无法纳入一个通用模型。另一方面，同向转运体中共转运的方向与角膜上皮和内皮、睫状体上皮以及视网膜色素上皮中的液体运输方向一致。
