Factor V binding to activated platelets.

In a representative experiment, gel-filtered human platelets were activated with 5 nmol/L thrombin (Panel A), 500 ng/mL convulxin (Panel B), 2 μmol/L A23187 (Panel C), thrombin plus convulxin (same concentrations; Panel D), thrombin plus A23187 (Panel E), or convulxin plus ionophore (Panel F) as described in “Materials and methods.” Surface-bound FV was detected with biotinylated monoclonal antibody HFV-237 against factor V and phycoerythrin-streptavidin (FL₂). In each panel, control platelets are indicated by the line histogram, and stimulated cells are depicted with the shaded histogram. Region M1 represents all cells binding FV, and region M2 represents cells binding very high levels of FV. Cells in region M2 are referred to as COAT-FV (see text). Experiments performed with antibody HFV-271 gave similar results to those for HFV-237 (data not shown).