INFLUENCE OF HYDRODYNAMIC IMPOSED SHEAR-STRESS ON THE ACTIVATION OF FACTOR-X IN THE PRESENCE OF TISSUE FACTOR FACTOR VIIA COMPLEX IN A CONTINUOUS-FLOW REACTOR

The effect of shear stress on the ability of tissue factor-factor VIIa complex to activate factor X in a continuous flow reactor was studied . Tissue factor immobilized in a phospholipid bilayer on the inner sur face of a capillary tube was exposed to a perfusate containing factors VIIa and X flowing at flow rates of 12.7, and 204 mu l/min, correspon ding to wall shear rates of 100, and 1760 sec(-1). The maximum flux (m oles formed per unit surface area per unit time) of factor Xa (activat ed form of factor X) produced at the wall decreased as the shear stres s at the wall was increased from 1 to 3 dynes/cm(2) (3-fold) at a cons tant shear rate of 100 sec(-1). In contrast, at higher shear rate (176 0 sec), increasing shear stress from 16 to 48 dynes/cm(2) had no signi ficant influence on factor Xa production. The decreased production of factor Xa at higher shear stress (low shear rate 100 sec(-1)) probably reflects the transport limitation of factor X to the wall. Apparently shear stress can directly influence the activation of factor X at low shear rates.