Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and
other solutes. Known as water channels, they are
integral membrane pore proteins (1, 2).
Aquaporin 4 is constitutively expressed in the basolateral
cell membrane of principal collecting duct cells in the
kidney and provide a pathway for water to exit these
cells (3). It is also expressed in astrocytes and is
up regulated by direct insult to the CNS (4).
Aquaporin 4 has been proposed as the primary
autoimmune target in neuromyelitis optica ( 5, 6).