Chloride and inorganic phosphate modulate binding of oxygen to bovine red blood cells

The influence of Pi and Cl on the equilibrium of oxygen binding to bovine red blood cells was assessed by plotting the whole blood oxygen dissociation curve measured under standard conditions with and without added KCl and K2HPO4. Both salts shifted the oxygen dissociation curve to the right. This effect was more marked at the highest saturation levels. At a given saturation level, the anion-induced shift was linearly related to the concentration of salt added to the blood. Cl had a greater effect than Pi. The relationship between changes in Po2 at 50% hemoglobin saturation (in Torr) and concentrations of ions added (in mmol/l) was equal to 0.0515[Cl] + 0.0302[Pi] (r2 = 0.94; P < 0.001). These changes were not due to the hyperosmolality induced by salt addition, since sucrose added in place of salts was without effect on the measured parameters. The oxygen exchange fraction expressed as percentage of saturation, i.e., the difference in hemoglobin saturation when Po2 decreases from 130 to 40 Torr, was linearly correlated to added anion concentration (in mmol/l) (= 0.102[Cl] + 0.059[Pi] (r2 = 0.95; P < 0.001)). No significant interaction between the anions was observed; their effects were purely additive. This original mechanism of controlling the oxygen affinity of bovine blood may have clinical relevance: Cl and Pi could be used to increase oxygen transport efficiency in hypoxic animals.