Critical role of aquaporin-4 (AQP4) in astrocytic Ca ²⁺ signaling events elicited by cerebral edema

Aquaporin-4 (AQP4) is a primary influx route for water during brain edema formation. Here, we provide evidence that brain swelling triggers Ca 2+ signaling in astrocytes and that deletion of the Aqp4 gene markedly interferes with these events. Using in vivo two-photon imaging, we show that hypoosmotic stress (20% reduction in osmolarity) initiates astrocytic Ca 2+ spikes and that deletion of Aqp4 reduces these signals. The Ca 2+ signals are...