The chloride shift occurs rapidly and is essentially complete in

Chloride Shift Since the rise in the HCO3– content of red cells is much greater than that in plasma as the blood passes through the capillaries, about 70% of the HCO3– formed in the red cells enters the plasma. The excess HCO3– leaves the red cells in exchange for Cl– , a process mediated by Band 3, a major membrane protein. This exchange is called the chloride shift. Because of it, the Cl– content of the red cells in venous blood is therefore significantly greater than in arterial blood. The chloride shift occurs rapidly and is essentially complete in 1 second.