Fig. 7. Protrusions and retractions are less active during shear-flow-induced cell motility in cells devoid of the beta subunit of the heterotrimeric G protein family. LW6 or LW20 cells undergoing shear-flow-induced motility (=2.4 Pa) in the presence of the indicated calcium concentration were imaged at high resolution under RICM and morphology of cell-substrate contact areas was analyzed as described in Materials and Methods. (A) Growth rates of gained (left) and lost (right) contact areas are represented as a function of time, for a single Gß-null cell at a 1 mM calcium concentration. (B,C) Mean peak height and frequency are plotted as a function of individual cell speed. , protrusions; , retractions. Filled symbols, Gß-rescued cells (LW20); open symbols, Gß-null cells (LW6). In B, the dotted line is a linear least square fit of the LW20 data points (slope 4.9 µm; ordinate at origin 0.7 µm² second^-1). Standard deviations for protrusion and retraction peak height are 0.9 and 0.7 µm² second^-1 for Gß-null cells and 0.7 and 0.5 µm² second^-1 for Gß-rescued cells, respectively. In C, the dotted lines represent the mean values of the retraction and protrusion frequencies.