FIGURE 8.

Off-rates (k_off) derived from lifetimes of transient tethers of L-selectin-bearing microspheres of 3- and 1-μm radii (a—c) or of unfixed or fixed neutrophils (d—f) to low-density sPSGL-1 (<10 sites/μm²) in the absence or presence of 6% Ficoll (which increased the medium viscosity by 2.6 fold) were plotted against wall shear rate (a and d), wall shear stress (b and e), and tether force (c and f). Low ligand density favors (but does not guarantee) single bonds. Tether lifetimes (∼100 measured at 4-ms temporal resolution under any given condition) are distributed as single exponential decays, consistent with first-order dissociation of single bonds. Plotting the data in semi-log scale linearizes the distribution. k_off can be evaluated from the negative slope of the linear fit to the data or from the average lifetime. Reproduced from Yago et al.²⁰