Use of a laminar flow chamber to study the rate of bond formation and dissociation between surface-bound adhesion molecules: Effect of applied force and distance between surfaces

It has recently been shown that much information on the behaviour of surfac e-bound adhesion molecules could be obtained by monitoring the motion of re ceptor-coated particles along ligand-derivatized surfaces in the presence o f a hydrodynamic force of a few pN. This procedure is expected to allow dir ect monitoring of the formation and dissociation of individual bonds. We pr esent experimental results on the interaction between streptavidin-coated s pheres (1.4 mu m diameter) and control or biotinylated mica surfaces in a l aminar flow chamber. Moving spheres are found to display numerous arrests w hose frequency is markedly increased (5-13-fold) in the presence of biotin groups. For a given shear rate, the binding frequency is strongly dependent on the sphere-surface separation. Indeed, this frequency displayed a 14-fo ld decrease when the velocity increased from 7 to 15 mu m s(-1) for a wall shear rate of 20 s(-1). Furthermore, the lifetime of observed arrests was o f the order of several seconds, i.e. 5-50-fold higher than previously deter mined on models such as selectin-ligand, CD2-CD48 or cadherin-cadherin. Fin ally, this lifetime did not decrease when the wall shear rate was increased from ca. 10 to 40 s(-1).