Fig. 3. Inhibition of calcium transients prevents retraction and cell movement but not the generation of traction stress. (A,B) Plots of the relative changes in traction stress (red), cell speed (green), cell shape (orange) and calcium indicator fluorescence (blue). Each graph was offset for clarity and values for shape factor were multiplied by 3, for illustrative purposes. The addition of EGTA (A) or Gd³⁺ (B) is indicated (arrow), as is the retraction (R). (C) IRM images of an entire cell moving in the direction indicated (bold white arrow), and insets showing a retracting cell margin on the right side, at various time points before and after the addition (bold black arrow) of EGTA. Regions of very close contact beneath the lamellipodium (white arrowheads) and retraction fibers at the retracting rear margin (black arrowhead) can be seen before EGTA addition. retraction fibers disappear, indicating a reduction in the rate of retraction. A region of very close contact at the rear cell margin begins to enlarge 30 seconds later (arrow) and becomes more distinct after 2-3 minutes, by which time retraction is inhibited. Bar, 10 µm.