Figure 2. Influence of shear stress on shearotactic cell migration.
(A) Influence on cell speed: probability density function (PDF) of the cell speed for five different magnitudes of the shearotactic signal with the associated average speed vs. shear stress in insert. For shear stress levels lower than 0.05 Pa, the average cell speed is of the order of the cell speed in the absence of any signal (insert). For values of 
in the range 0.18 to 0.5 Pa, the average cell speed is found to be almost constant. This conclusion, established on the sole basis of first-order statistics of cell speed, is readily generalized by noticing the similarities in the PDFs of cell speed for 0.05 Pa on the one hand, and for 0.18 Pa on the other hand. (B) Evolution of the shearotactic directionality with the shear stress. (C) Evolution of the 
with the shear stress. 
is a measure of the instantaneous ability of the cell to migrate in the signal's direction, while 
is an integrated measure of 
throughout the entire cell path. This subtle relationship between 
and 
is reflected in the above variations with the shear stress where a plateau about 0.9 is reached for 
0.18 Pa. For all values of 
, only cells adhering to the substrate throughout the entire duration of the experiment were considered and analyzed. All experiments were conducted with a soluble concentration of calcium, [Ca2+]ext, set and fixed at 3 mM and cells are crawling over a plastic hydrophobic surface.