Dibas A I, Mia A J, Yorio T
Department of Pharmacology, University of North Texas Health Science Center at Fort Worth, Fort Worth, Texas 76107, USA.
Proc Soc Exp Biol Med. 1998 Dec;219(3):183-99. doi: 10.3181/00379727-219-44332.
The discovery of water channels (aquaporins) was a breakthrough in research on water transport. Aquaporins are a family of intrinsic membrane proteins that function as water-selective channels (except aquaporin-3 and aquaporin-7, which are permeable to urea and glycerol as well) in the plasma membranes of many cells. Aquaporin-0 (MIP26) functions to maintain fluid balance in the lens. Aquaporin-1 is involved in water reabsorption in the kidney's proximal tubules and the thin descending Henle's loop, aqueous humor formation in eye, cerebrospinal fluid formation in brain, and airway hydration in lung. Aquaporin-2 is the only water channel that is activated by vasopressin to enhance water reabsorption in the kidney collecting duct. Aquaporin-3 also contributes to water reabsorption in the kidney collecting duct but is unresponsive to vasopressin. It also appears that aquaporin-3 may contribute to cornea transparency. Aquaporin-4 is involved in cerebrospinal fluid transport in brain, water transport in the kidney collecting duct, aqueous humor transport in the eye, and airway hydration in the lung. Aquaporin-5 apparently is coupled to fluid secretion in exocrine tissues. Although the exact function of aquaporin-6 is not known due to its uncertain localization, its restricted presence in the kidney may suggest a potential role in water transport. Aquaporin-7 appears to play a role in the cryopreservation of the sperm whereas aquaporin-8 is responsible for the secretion of pancreatic juice. The major focus of this review is a discussion of aquaporins in renal epithelia, and particularly the mechanisms associated with vasopressin-mediated water transport involving aquaporin-2 and the signal transduction pathways linked to vasopressin action.
水通道（水孔蛋白）的发现是水运输研究中的一项突破。水孔蛋白是一类内在膜蛋白家族，在许多细胞的质膜中作为水选择性通道发挥作用（水孔蛋白-3和水孔蛋白-7除外，它们也可通透尿素和甘油）。水孔蛋白-0（MIP26）的功能是维持晶状体中的液体平衡。水孔蛋白-1参与肾脏近端小管和髓袢降支细段的水重吸收、眼房水生成、脑脑脊液生成以及肺气道水合作用。水孔蛋白-2是唯一一种受血管加压素激活以增强肾脏集合管水重吸收的水通道。水孔蛋白-3也有助于肾脏集合管的水重吸收，但对血管加压素无反应。水孔蛋白-3似乎也有助于角膜透明。水孔蛋白-4参与脑内脑脊液运输、肾脏集合管水运输、眼房水运输以及肺气道水合作用。水孔蛋白-5显然与外分泌组织中的液体分泌有关。尽管由于水孔蛋白-6定位不确定，其确切功能尚不清楚，但其在肾脏中的有限存在可能提示其在水运输中具有潜在作用。水孔蛋白-7似乎在精子冷冻保存中起作用，而水孔蛋白-8负责胰液分泌。本综述的主要重点是讨论肾上皮中的水孔蛋白，特别是与血管加压素介导的涉及水孔蛋白-2的水运输相关的机制以及与血管加压素作用相关的信号转导途径。
