Figure 1

Structural organization of AQP4 in the astrocyte membrane. (A) Schematic drawing of the AQP4 homo-tetramer assembly within the lipid membrane from a lateral view resulting in a central pore permeable to cations and gases (green arrows) [16]. Each individual aquaporin facilitates bi-directional water movement that is dependent on the osmotic gradient (blue arrows) (modified from Badaut et al. [57]). (B) In normal brain, association between AQP4-m1 (red circles) and AQP4-m23 (blue circles) isoforms contribute to form orthogonal array of particles (OAPs). Higher expression of AQP4-m23 contributes to the formation of large OAPs, and should facilitate the gas, ion (green arrows), and water diffusion (water arrows) through the astrocyte membrane. (C) In brain injury, increase of AQP4-m1 [19] should contribute to disruption of OAPs (modified from Badaut et al. [57]). Changes in OAP size may decrease the number of central pore and possibly affect not only water movement but also the ion and gas movements.