Effect of hypoxia on ATP release and cell lysis. (A) Average ATP (left) and hemolysis (right) in control and hypoxia-treated RBCs. Each bar represents an average of 12 or 13 samples ± SEM from 4 independent experiments performed with the same blood batch, *Statistically significant difference compared with the controls (P < .05, Mann-Whitney U test). (B) Relationship between extracellular ATP and hemolysis. The graph shows tight, linear correlation (P < .0001) between hemolysis extent (depicted as absorbance – left axis, or % hemolysis – right axis) and ATP release induced by hypoxia for all data points of the 4 independent experiments reported in A. Each experiment is represented by a different symbol, with black symbols referring to hypoxia and open symbols indicating the control (normoxia) condition. The slope of linear fit corresponds to intracellular ATP concentration of 1.98 mM.