Physiological consequences of oxygen-dependent chloride binding to hemoglobin.

The PO(2)-dependent binding of chloride to Hb decreases the Cl(-) concentration of the red blood cell (RBC) intracellular fluid in venous blood to approximately 1-3 mmol/l less than that in arterial blood. This change is physiologically important because 1) Cl(-) is a negative heterotropic allosteric effector of Hb that competes for binding sites with 2,3-bisphosphoglycerate and CO(2) and decreases oxyhemoglobin affinity in several species; 2) it may help reconcile several longstanding problems with measured values of the Donnan ratios for Cl(-), HCO, and H(+) across the RBC membrane that are used to calculate total CO(2) carriage, ion flux rates, and membrane potentials; 3) it is a factor in the change in the dissociation constant for the combined nonvolatile weak acids of Hb associated with the Haldane effect; and 4) it diminishes the decrease in strong ion difference in the RBC intracellular fluid that would otherwise occur from the chloride shift and prevent the known increase of HCO concentration in that compartment.