Leukocyte rolling velocity and its relation to leukocyte-endothelium adhesion and cell deformability

To explore the relationship between the rolling velocity of leukocytes (V-WBC) and wall shear rates (gamma over dot), measurements of V-WBC were made along the length of rat mesenteric venules in which a gradient in gamma over dot was induced by compressing the venule with a blunted microprobe to form a stenosis in which gamma over dot varied from 300 to 1500 s(-1). For individual WBCs that rolled through the stenosis, V-WBC was proportional to gamma over dot for its entire range, in contrast to previous studies that have shown a plateau in V-WBC vs. gamma over dot for the ensemble population. Comparisons of the slope of V-WBC vs. gamma over dot for individual cells with ensemble values of V-WBC/gamma over dot Obtained in the entrance region of the stenosis were made during suffusion of the tissue with the chemoattractant N-formylmethionyl-leucyl-phenylalanine (FMLP), to increase WBC-EC adhesion and WBC stiffness, or colchicine and cytochalasin B to increase WBC deformability. Under control conditions, the slope of individual cells was significantly 20% greater than V-WBC/gamma over dot, whereas it was significantly reduced by 48% during suffusion with FMLP. With exposure to colchicine, the slope was 78% lower than V-WBC/gamma over dot and compared with control was similar in magnitude to that obtained with FMLP. Cytochalasin also reduced the slope by 22% compared with control and 34% compared with V-WBC/gamma over dot. The diminished slopes of V-WBC vs. gamma over dot were consistent with published theoretical models that suggest a reduced slope with increased strength of adhesion or WBC deformability. It is thus concluded that the apparent plateau in V-WBC vs gamma over dot arises due to the heterogeneity of adhesive and/or deformability properties of the ensemble population of circulating WBCs.