Biology :: Cell Membrane Transport :: Aquaporins
Aquaporins are selective membrane channel proteins found in the lipid bilayer of living cells that work to transport water across the cell membrane. Aquaporins accomplish this task while excluding any unwanted ions or other polar molecules.
Aquaporins is a class of integral membrane proteins that form pores in the membrane of biological cells and selectively conduct water molecules in and out, while preventing the passage of ions and other solutes.
This "first" water channel was originally named CHIP28 and is now known as aquaporin 1. They are each composed of four (typically) identical subunit proteins. Water molecules traverse the narrowest portion of the channel single file.
The presence of water channels increases the permibility of membranes to water by as much as ten fold. There are currently 13 known aquaporins in mammals, distributed in most tissues, but many more have been identified in lower organisms and in the plant kingdom.