Effect of temperature on rate of CO2 uptake by human red cell suspensions

The time course of carbon dioxide uptake by oxygenated supensions of human red cells was followed using a CO2 electrode in a Hartridge-Roughton continuous-flow rapid-reaction apparatus. Measurements were made at several temperatures from 1i to 42 degrees C, with the initial PCO2 in the reacting mixture from 40 to 60 mmHg. The initial part of the uptake curve is presumably rate limited by the intracellular hydration of CO2 with reaction-velocity constants in cell water from 280 to 960 S-1 at 42 degrees C and an activation energy of 2.4 kcal mol-1. The later stages of CO2 uptake were much slower, with half-times from greater than 1.5 s at 12 degrees C to 0.7 s at 42 degrees C, and were presumably rate limited by the chloride-bicarbonate shift and H+ interchanges. The results indicate that despite the acceleration of the hydration reaction in cell water by a factor of 5,000 at 37 degrees C and 3,800 at 42 degrees C, the later part of the exchange is too slow to permit blood to come intoC02, equilibrium with actively exercising muscles during its passage through the capillary bed.