Procoagulant phospholipid externalization and membrane vesiculation in calcium ionophore-stimulated RBC from 4 PNH patients (P) and 2 healthy subjects (T) measured by prothrombinase assay. Cells were stimulated by 5 μmol/L calcium ionophore A23187 in the presence of 2 mmol/L external CaCl2 for 90 minutes at 37°C. Stimulated cells were centrifuged for 30 seconds at 12,000g. Microparticle release was measured in the supernatant, whereas phosphatidylserine externalization was measured on the pelleted cells. Data (n = 3) represent the increase of prothrombinase activity after stimulation and are expressed as the ratio between the activity before and after ionophore stimulation. The basal activity of the RBC before stimulation was 2.2, 4.5, 0.6, 0.2, 1.0, and 0.3 nmol/L phosphatidylserine equivalent for P1, P2, P3, P4, T1, and T2, respectively. In the supernatant, corresponding basal activities were measured at 1.2, 1.3, 0.4, 0.2, 0.4, and 0.4 nmol/L phosphatidylserine equivalent.
