Bohr shift by lactic acid and the supply of O2 to skeletal muscle.

Conditions simulating changes during physical exercise were induced in erythrocytes to determine the resulting Bohr effect. Lactic acid was added to red cell suspensions and whole blood with initial 25 and 60% SO2, at 42 Torr PCO2, and temperatures of 20 and 37 degrees C. Changes in pH, PO2 and SO2 were measured. CO2 liberation from buffering lactic acid in the extracellular fluid and its diffusion into erythrocytes resulted in an exaggerated Bohr shift, if the gas could not escape from the liquid phase (closed system, 'muscle' conditions). PO2 at constant SO2 increased by up to 11.7%.mmol-1.L lactic acid. After reequilibration to initial PCO2 values (open system, 'lung' conditions) the Bohr shift decreased (remaining PO2 increase 0.7-1.4%.mmol-1.L) mainly caused by the reduced acidification. In addition, the Bohr coefficients (BC) under closed conditions were larger (-0.36 to -0.50) than after reequilibration (-0.20 to -0.38). This difference is attributed to a larger CO2 BC than fixed acid BC. These effects might be enhanced in vivo by temperature differences between muscle and lung, lowered nonbicarbonate buffering of blood and counter-current blood flow in muscle.