Dependence of purine loss from human erythrocytes on external pH

Human red cells were incubated at 37 degrees C in physiological saline at pH 7.4 with 8-3H-adenine to label the adenine nucleotides. After washing, the cells were incubated in similar salines which were buffered to different values of pH. The loss of radioactivity from cells into medium was very slow below pH 7.4 and accelerated greatly with increasing pH up to about 7.8. At that pH the loss increased for at least 3 h when it represented more than 30% of the initial radioactivity of the cells. The loss could not be accounted for by haemolysis which remained minimal. The extracellular radioactivity was present mostly in hypoxanthine and some inosine. The loss of purine did not depend on oxygenation of the cells. These results, together with the high-affinity uptake system for adenosine, could provide a partial explanation of the turnover of adenine nucleotide purines of red cells which is many times faster than that of the cells themselves.