Fig. 14

Types of transporters that load or extrude acid from brain endothelial cells. In the presence of CO₂/HCO₃ ⁻ acid is added (i.e. HCO₃ ⁻ is removed) primarily by either Cl⁻/HCO₃ ⁻ exchange (AE: AE2 and possibly AE3) or a Na⁺, HCO₃ ⁻ cotransporter operating in a 3:1 mode (NBC: probably NBCe1). Acid is extruded by Na⁺ driven transport by several Na⁺, HCO₃ ⁻ cotransporters either Cl⁻-independent (NBC: e.g. NBCn1 (n = 1) and NBCe1 in a 2:1 mode (n = 2) or Cl⁻-dependent (NDCBE-like). In the absence of CO₂/HCO₃ ⁻ the principal loader is here called the “leak” and the principal extruder is a Na⁺/H⁺-exchanger (NHE). The classification into loaders and extruders follows that used in [399, 545]