Respiratory oxidation in the mitochondria produces carbon dioxide (CO2) as a waste product. CO2 is in equilibrium with bicarbonate (HCO3-) and is the body's central pH buffering system. HCO3- is charged so cannot move across membranes unaided. The bicarbonate transport proteins move bicarbonate across the membrane. There are 14 genes which encode these transport proteins in mammals. Applying the Human Genome Organization's sytematic nomenclature to human genes, the bicarbonate transporters belong to the SLC4A and SLC26A families. Within SLC4A, there are two distinct subfamilies, functionally corresponding to the electroneutral Cl-/HCO3- exchangers and Na+-coupled HCO3- co-transporters (Romero MF et al, 2004; Cordat E and Casey JR, 2009).