Reduction of oxylabile CO₂ in human blood by lactate

The influence of lactic acid, hydrochloric acid, and sodium lactate addition (10 mmol/l each) on oxylabile CO₂ was investigated in blood of male subjects after equilibration at 37°C with 3, 6, and 10% CO₂ in N₂ and O₂, respectively. The total CO₂, pH in whole blood and erythrocytes, oxygen saturation, hemoglobin concentration, and hematocrit value were measured. With these data we calculated bicarbonate and carbamate concentrations and the corresponding differences between oxygenated and deoxygenated blood. The amount of oxylabile bicarbonate was not systematically influenced by the various experimental conditions. The carbamate content, however, was larger in deoxygenated than in oxygenated blood (up to 0.08 mol/mol hemoglobin) only in the absence of lactate. In the presence of lactic acid as well as sodium lactate, the carbamate content in oxygenated blood was higher by 0.06-0.13 mol/mol hemoglobin than in deoxygenated blood. The lactate effect even increased after 2,3-diphosphoglycerate depletion. We suggest, therefore, a competition between CO₂ and the lactate ion at the NH₂-terminal valine of the β-globin chain in deoxygenated hemoglobin.