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 surface-bound adhesion molecules could be obtained by monitoring the motion of receptor-coated particles along ligand-derivatized surfaces in the presence of a hydrodynamic force of a few pN. This procedure is expected to allow direct monitoring of the formation and dissociation of individual bonds. We present experimental results on the interaction between streptavidin-coated spheres (1.4 microns diameter) and control or biotinylated mica surfaces in a laminar flow chamber. Moving spheres are found to display numerous arrests whose 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-fold decrease when the velocity increased from 7 to 15 microns s-1 for a wall shear rate of 20 s-1. Furthermore, the lifetime of observed arrests was of the order of several seconds, i.e. 5-50-fold higher than previously determined on models such as selectin-ligand, CD2-CD48 or cadherin-cadherin. Finally, this lifetime did not decrease when the wall shear rate was increased from ca. 10 to 40 s-1.