Aquaporins and aquaglyceroporins are membrane channels that allow the permeation of water and certain other small solutes across the cell membrane. Since the isolation and cloning of the first aquaporin (AQP1) [3], 12 additional members of the family have been identified, although little is known about the functional properties of two of these (AQP11 (ENSG00000178301) and AQP12 (ENSG00000184945)). The other 11 aquaporins can be divided into two families (aquaporins and aquaglyceroporins) depending on whether they are permeable to glycerol [2]. One or more members of this family of proteins have been found to be expressed in almost all tissues of the body. Individual AQP subunits have six transmembrane domains with an inverted symmetry between the first three and last three domains [1]. Functional AQPs exist as tetramers but, unusually, each subunit contains a separate pore, so each channel has four pores.

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1. Castle, NA. (2005) Aquaporins as targets for drug discovery. Drug Discov. Today, 10 (7): 485-93. [PMID:15809194]

2. King, LS; Kozono, D; Agre, P. (2004) From structure to disease: the evolving tale of aquaporin biology. Nat. Rev. Mol. Cell Biol., 5 (9): 687-98. [PMID:15340377]

3. Preston, GM; Carroll, TP; Guggino, WB; Agre, P. (1992) Appearance of water channels in Xenopus oocytes expressing red cell CHIP28 protein. Science, 256 (5055): 385-7. [PMID:1373524]

4. Yasui, M; Hazama, A; Kwon, TH; Nielsen, S; Guggino, WB; Agre, P. (1999) Rapid gating and anion permeability of an intracellular aquaporin. Nature, 402 (6758): 184-7. [PMID:10647010]