AQP4 and central nervous system cancer: AQP4-facilitated glioma invasion is dependent on co-expression of chloride channels (ClC2) and the potassium-chloride co-transporter 1 (KCC1) in invadopodia, which could provide the ionic driving force for water efflux leading to cell shrinkage that could augment invasiveness through ECM (Mcferrin and Sontheimer, 2006; McCoy et al., 2010).