SLC9A1 and neoplasm: In addition, different transporters/pumps are involved in the regulation of tumor pHi and pHe, including monocarboxylate transporters 1–4 (MCT), the Na+/H+ exchanger 1 (NHE1), HCO3− transporters (NBCs), vacuolar ATPases (V-ATPase) as well as different carboanhydrases (CAII, CAIV, CAXII)12,17–19.