Figure 1.

Effect of xanthine oxidase and hypoxanthine (XO/HO) mixtures on accumulation of reactive oxygen species (ROS) and phosphatidylserine (PS) exposure in red cells from patients with sickle cell anaemia (SCA). (A) Red cells were pre‐loaded with CM‐H₂DCF‐DA (100 μmol/l) to measure ROS levels [as median fluorescence intensity (MFI)] or treated with the same final concentration of dimethyl sulphoxide [DMSO] (control) before incubation with hypoxanthine (HO, 2 mmol/l) and xanthine oxidase (XO, 0–0·1 U/ml) mixtures for 30 min at 37°C (n = 2). (B) Red cells were permeabilised to Ca²⁺ with the ionophore bromo‐A23187 (6 μmol/l), and incubated in different free [Ca²⁺]_os, maintained using Ca²⁺ / 2 mmol/l EGTA mixtures, at 0·5% haematocrit for 30 min at 37°C in the absence (filled circles) or presence (open circles) of HO (2 mmol/l)/XO (0·015 U/ml) mixtures after which externalised PS was labelled with LA‐FITC, n = 8. PS exposure was normalised to that of control red cells at 1 μmol/l free [Ca²⁺]_o (31·1 ± 3·9% of total red cells). Symbols represent means ± SEM for red cells from n different individuals. *P < 0·05; **P < 0·005.