Water channels edema

Doczi et al., 1984 Laszlo et al., 1999), and cold-induced vasogenic edema (Ikeda et al., 1997b Bemana and Nagao, 1999). There is a relationship between AVP and AQP in the kidney, but the interaction between AVP and water channels in the brain remains to be elucidated. 

Aquoporins are water channels that mediate rapid osmotically driven water transport across ceU membranes (Preston et al., 1992 Agre et al., 2002 Badaut et al., 2002). Brain tissues, including microvessels, contain relatively high levels of aquaporins. In particular, Aquaporin 4 (AQP4) is abundantly expressed in the brain, mainly in astrocytes, which are commonly observed to be swollen during cerebral edema (Jung et al., 1994 Kimelberg, 1995 Nielsen et al., 1997). 

The forces driving water flow to form cytotoxic edema are osmotic, generated in brain injury conditions (ischemia, trauma, hypoxia) by disturbances in ionic homeostasis due to failure of the Na /K+ ATPase and/or dramatic influx of Na" and Ca " via ionotropic glutamate receptors (excitotoxicity) and other ionic channels. These pathological alterations in cellular ionic homeostasis result in Na" " and water flow from the intravascular and extracellular space into the intracellular compartment. 

---