Figure 2.

Prothrombinase activity in intact (A and B) or hypotonically lysed (C) red cells from patients with sickle cell anaemia. Red cells were treated as in Fig 1B with thrombin formation used as a measure of accessible phosphatidylserine (PS). (A) Thrombin formation in the absence (filled circles) or presence (open circles) of HO (2 mmol/l)/XO (0·015 U/ml) mixtures over a range of free extra cellular [Ca²⁺] ([Ca²⁺]_o; 0·1–10 μmol/l), with thrombin formation per min normalised to that of control red cells at 1 μmol/l free [Ca²⁺]_o. (B) Thrombin formation in the absence (control) or presence of HO (2 mmol/l)/XO (0·015 U/ml) mixtures or PMS (0·1 mmol/l), given as a percentage relative to the total value in lysed red cells at two different free [Ca²⁺]_os (0·1 and 1 μmol/l), indicative of prothrombin activity due to externalised PS present on only the outer bilayer of the red cell membrane. (C) Total thrombin formation at 0·1 and 1 μmol/l free [Ca²⁺]_o in the absence and presence of HO (2 mmol/l)/XO (0·015 U/ml) mixtures or PMS (0·1 mmol/l) as measured by thrombin formation (in arbitrary units, AU) of hypotonically lysed red cells to give prothrombin activity of total PS present on both the inner and outer bilayers of the red cell membrane. Symbols and histograms represent means ± SEM for red cells from 4 to 5 different individuals. *P < 0·05; **P < 0·005.