[The molecular biology studies of water channels]

Water channels are the aqueous pores in the plasma membranes of mammalian and plant tissue cells. The cDNA sequence of the first water channel protein (AQP-CHIP) was reported in 1991. Up to date, at least five mammalian water channels are identified and referred to as the "aquaporin" (AQP). AQPs are the members of major intrinsic protein (MIP) family. Channel-mediated water transport permits the movement of water in the direction of an osmotic gradient. The distributions of AQPs are in many tissues and most of them are expressed in the renal medulla. AQP-CHIP assembles into homotetramers in the plasma membrane and each CHIP monomer appears to form a functional water pore.