Rate of the Bohr shift in human red cell suspensions

Abstract

We have measured the rate at which the O2 tension rises in a partially oxygenated suspension of normal human red cells at 37 C as a result of a sudden rise in CO2 tension (the Bohr shift) in a Hartridge-Roughton rapid reaction apparatus. A Teflon covered platinum electrode was used to measure O2 tension. The rise in O2 tension had an average half time of 0.12 sec following increments of 18–65 mm Hg in CO2 tension in twelve experiments on the blood of three normal individuals. The comparable movement of O2 out of the red cell as a result of a decrease in ambient O2 tension at a constant CO2 tension had an average half time of 0.012 sec in four experiments on the blood from the same three subjects. This suggests that the velocities of the reactions of CO2 are rate-limiting in the Bohr shift. Acetazolamide (10-3 m) slowed the rate of the Bohr shift to less than one-seventh; no measurable change in O2 tension occurred until about 0.03 sec. measurable change in O2 tension occurred until about 0.03 sec. Submitted on July 2, 1962

Synergism in the kinetic reactions of O2 and CO2 with human red blood cells*

“…In terms of whole blood these concentrations were about 50 mg/100 ml., far more than is generally believed Table 3 (series IV) as initial rate (% 02Hb change per second) and as t50. The initial rates and t50 are slightly less than those reported by Craw et al (1963). Since we shifted the pH upwards and they shifted the pH downwards, it appears that the rate of the Bohr shift is about the same in both directions.…”

“…If the chemical reaction is directly involved in the interaction with CO2 observed in the intact cell the effect is more likely to be due to slowing of the association reaction with decreasing pH than to acceleration of the dissociation reaction. We are emphasizing the pH effect of CO2 (hydration) because the acetazolamide experiments reported here and by Craw et al (1963) effectively rule out any significant direct or uncatalysed action of CO2 such as physically dissolved CO2 or carbamino formation on the O2Hb reaction kinetics under the conditions of the experiments.…”

“…Assuming transit times at rest in systemic capillaries to be about the same as in the pulmonary circuit, say 0 75 sec, there is adequate time for both the deoxygenation reaction and the slower Bohr shift reaction to be completed separately (Craw et al 1963). However in exercise, when the red cells move more rapidly through the capillaries, there might not be time enough for the two successive reactions to be completed so that the venous PO, and Pco0 would incorrectly reflect the end-capillary partial pressures (Forster, Craw, Constantine & Morello, 1962).…”

“…There are no data in the foregoing on the Bohr shift reaction, but only on the C02 hydration and carbamino reactions that provide the basis for it. Craw, Constantine, Morello & Forster (1963) studied the actual kinetics of the Bohr shift in dilute human red cell suspensions. They found the Bohr shift to be relatively slow (t50 -0-12 Defares & Visser (1962) and Bernard (1960,1961).…”

A comparative study of the kinetics of the Bohr effect in vertebrates.

“…However in blood, the generation of the Bohr effect must also include the diffusion of CO2 and 02 through the red cell membrane and cytoplasm and the intracellular hydration-dehydration reactions of C02. The kinetics in intact human red cells have been studied by Craw, Constantine, Morello & Forster (1963) and Forster & Steen (1968). They showed the process has a half-time of 120 msec, a rate sufficient to yield equilibrium in 0-75-1 sec, the average capillary transit time.…”