Estimation of the platelet glycoprotein (GP) Ib - von Willebrand factor (vWf) bond lifetime under hydrodynamic flow

The interaction between the platelet glycoprotein (GP) Ib and von Willebrand factor (vWf) is crucial in hemostasis and thrombosis. Here, we investigated the kinetics of this interaction under flow conditions. Chinese hamster ovary (CHO) cells expressing the GP Ibα receptor were perfused through a parallel-plate flow chamber over coverslips coated with vWf-A1 at concentrations below those that will support cell rolling. Under these conditions, the cells formed transient tethers with the matrix, after which they detached and rejoined the bulk flow. The events were recorded in realtime with a video microscope and later analyzed by digital image processing. We fitted a first-order kinetic model for bond dissociation to the tether time distribution and estimated an off-rate constant (k_off) at different shear stresses. The k_off showed a weak exponential dependence on the shear stress. We also have compared k_off obtained by using different definitions of transient tether that exist in the literature, based on distance and instantaneous velocity plots.