Increased cell surface TF coagulant activity associated with HgCl₂ treatment could be explained by increased anionic phospholipids at the cell surface. (A) MDA 231 cells were treated with various concentrations (Conc.) of HgCl₂ for 15 minutes. After 15 minutes, HgCl₂ was removed, and cells were washed once before adding FVIIa (10 nM) and factor X (FX; 175 nM). Cell surface TF-FVIIa coagulant activity was measured as its ability to activate FX. (B) MDA 231 cells were treated with HgCl₂ as described in (A), and cell surface prothrombinase activity was measured by adding FXa (1 nM), FVa (10 nM), and prothrombin (1.4 μM) and then measuring the rate of thrombin generation. (C) MDA 231 cells were exposed to control vehicle or annexin V (200 nM) before they were treated with HgCl₂ (25 μM) for 15 minutes, and cell surface TF activity was measured as described in panel A. (D) MDA 231 cells were treated with a control vehicle for 15 minutes (○); annexin V (200 nM) for 15 minutes (□); a control vehicle for 15 minutes followed by HgCl₂ (50 μM) for 10 minutes (•); and annexin V (200 nM) for 15 minutes followed by HgCl₂ (50 μM) for 10 minutes (■). After the removal of HgCl₂, monolayers were incubated with ¹²⁵I-FVIIa (10 nM) (annexin V was added along ¹²⁵I-FVIIa to the cells that were preincubated with annexin V). ¹²⁵I-FVIIa bound to cells at various times was determined as described in an earlier publication.³⁰  (E) MDA 231 cells were pretreated with control buffer or control vehicle (Et.OH) or various concentrations of DTNB for 15 minutes before they were exposed to control vehicle or HgCl₂ (25 μM) for 15 minutes. Cell surface TF activity was determined as described in panel A. (F) MDA 231 cells were exposed to various concentrations of reduced glutathione for 15 minutes before their cell surface TF activity was determined as in panel A. (A-F) Data are expressed as mean plus or minus SEM (n = 3). *denotes the value significantly (P < 0.05) differs from the control value.