Activity and inhibition of the intrinsic tenase complex. Assays were performed using either adherent (left panels) or suspended cells (right panels). Apoptosis was induced by treatment with staurosporine (left panels, solid triangles) or culture in suspension with serum deprivation (right panels, shaded triangles) for 4 and 16 hours, respectively. The activity of the intrinsic tenase complex was determined by measuring the amidolytic activity of factor Xa after the addition of factor IXa, factor VIII, and factor X (A and B). The effect of the exposure of PS on the activity of the intrinsic tenase complex was assessed by the ability of annexin V to inhibit factor Xa formation (C and D). After preincubation of HUVECs with various concentrations of annexin V for 5 minutes, the activity of the intrinsic tenase complex was measured as described above. Controls were untreated cells (all panels; ○). Results are expressed as means ± SD (n = 4).