Activation of factor IX by erythrocyte membranes causes intrinsic coagulation.

As an extension of our earlier work, procoagulant activity of erythrocyte [red blood cell (RBC)] membrane was examined using biochemical and rheological techniques. Western blot analysis of coagulation factors incubated with erythrocytes (RBCs) showed that only factor IX (FIX) was activated by RBC membranes in the presence of calcium ions. A fluorogenic assay suggested that activated FIX is capable of activating factor X. A preliminary crude extraction of the substance from RBC membranes suggested that a FIX-activating enzyme may be located on the RBC membrane. The initiation of FIX activation by RBCs was enhanced by an elevation in hematocrit. Moreover, the rate of FIX activation by RBCs from normal pregnant women and diabetic patients was much faster than that from normal subjects. In addition, glucose treatment of normal RBCs resulted in the increase in procoagulant activity. It is suggested that FIX activation by RBC membranes may serve as a triggering mechanism for blood coagulation, although further study will be required to clarify the putative FIX activating enzyme on the RBC membrane and to permit more extensive physiological experiments to be performed.