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Fig. 6. Cells devoid of the ß subunit of the heterotrimeric G protein family are insensitive to an increase of the external calcium concentration. (A) Average speed of LW6 Gß-null cells (Gß
, 
) or LW20 Gß-rescued cells (Gß-rescued Gß, 
) is plotted as a function of the free calcium concentration in the flowing fluid (
=2.4 Pa). The solid line corresponds to a fit with an apparent calcium affinity of 150 µM and a minimum and maximum speed of 3.5 and 13 µm minute-1, respectively. (B) LW20 (Gß-rescued Gß, ) and LW6 (Gß, ) cells were allowed to adhere to glass at a low (5 µM) calcium concentration, then a constant shear stress (2.4 Pa) was applied and video recording started (t=0 minutes). After 2 minutes, the calcium concentration was raised to 1 mM at the same shear stress. Instant cell speed is plotted as a function of time. Note that at low calcium concentrations, LW6 cell speed is slightly, but significantly higher than that of LW20 cells. (C,D) Average cell speed (C) and directionality (D) are plotted as a function of the applied shear stress at a 1 mM calcium concentration either for LW20 (Gß-rescued Gß, triangles) or LW6 (Gß, ) cells. Average cell speed and directionality are determined from the steady-state portion of the motility response to shear stress.
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