AQP4 and brain ischemia: Knock-out of AQP4 or disruption of its polarized expression pattern mitigated the brain water accumulation associated with brain ischemia, water intoxication, and hyponatremia [3, 4, 6, 22, 47], suggesting that during pathophysiological conditions, AQP4 is a main entrance route for water from the plasma and into the brain.