Activation of factor IX in an umbilical vein model was established to result solely from factor VIIa/tissue factor (TF) activity generated within the umbilical vein wall, and the model was then used to study regulation of such extravascular factor VIIa-TF complexes. Vein segments were filled with a reaction mixture containing factor VIIa, Ca2+, a substrate, either [3H]factor IX or [3H]factor X,...
