SLC12A5 and glioblastoma: High-grade GBM cells are associated with increased intracellular chloride [Cl−]i level [26], which is associated with increased Na+-K+-Cl− co-transporter-1 (NKCC1, encoded by SLC12A2) and decreased K+-Cl− co-transporter (KCC2, encoded SLC12A5) activity [48,49].