Fig. 8. Shear-flow-induced motility of IP₃-receptor null Dictyostelium cells. (A,B) Average speed (A) and directionality (B) of IP₃-receptor null cells (IP₃-Receptor , circles) or parental RK-Ax2 cells (wild type, triangles) are 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 120 µM and a minimum and maximum speed of 5 and 32 µm minute^-1, respectively. The dotted line is a guide for the eye. (C,D) IP₃-receptor null cells (IP3-Receptor , ) or parental Ax2-RK cells (wild type, ) were allowed to adhere to glass at a low (5 µM) calcium concentration, then a constant shear-flow (2.4 Pa) was applied and video recording started (t=0 minutes). After 3 minutes, the calcium concentration was raised to 1 mM under the same shear stress. (C) Cell speed is plotted as a function of time. The lines are hand-drawn. (D) Cell directionality is measured during the 1-3 minutes (white bars) and 8-12 minutes (black bars) portions of the recordings, corresponding to a 5 µM and 1 mM extracellular concentration, respectively.