The rate of the `root shift' in eel red cells and eel haemoglobin solutions

1. We have measured the rate of the exchange of O 2 between eel red blood cells and their suspending fluid in a modified Hartridge—Roughton continuous-flow rapid-reaction velocity apparatus using an oxygen electrode to follow the progress of the reaction. 2. The half-times for the uncomplicated oxygenation and deoxygenation reactions in red cells at 24° C were approximately 0·025-0·08 sec. 3. The rate of the Root shift in cell suspensions varied widely, depending on the initial condition of the CO 2 -bicarbonate buffer system in the suspending fluid, with the rate of oxygenation or deoxygenation of the intracellular haemoglobin as an upper limit. ( a ) The most rapid Root shift was produced by a change in extracellular P CO 2 with minimal contributions from CO 2 hydration—dehydration reactions in the suspending fluid or from ion exchanges across the membrane, and had a half-time as short as 0·040 sec. ( b ) The slowest Root shift was produced by an increase in the extracellular lactic acid concentration in the absence of any form of CO 2 or in the presence of acetazolamide. This process is presumed limited by the rate of H + or OH - transfer across the membrane and had a half-time in excess of 10 sec. ( c ) The Root off-shift produced by an increase in P CO 2 plus a decrease in extracellular pH showed no significant trend as temperature was lowered from 30° to 11° C. ( d ) The Root on-shift produced by a decrease in P CO 2 and increase in extracellular pH had a half-time of 3 sec at 30° C, 9 sec at 24° C and 20 sec at 11° C. These changes appeared limited by the uncatalysed rate of extracellular CO 2 hydration. 4. Root off- and on-shifts in cell haemolysates at 24° C, produced predominantly by changing pH but with unavoidable subsequent readjustments of the CO 2 -bicarbonate buffer systems, had an initial rapid phase with half-times as low as 0·01 sec. However, the curves were not monotonic, although they became so in the presence of carbonic anhydrase, indicating partial rate limitation by CO 2 reactions.