Fig. 4. Response of cell migration and traction forces to the application of EGTA. Phase contrast images (A-C) of a migrating NIH3T3 fibroblast, recorded immediately before (A) and after (B,C) the application of 5 mM EGTA, showed inhibition of local protrusive activities, and partial retraction. Asterisks mark a fiduciary reference point on the substratum. The corresponding traction stress images showed a striking decrease in traction forces (D-F). Different colors represent the magnitude of traction stress, from 9.5x10¹ dynes/cm² (violet) to >1.00x10⁵ dynes/cm² (red). Scale bar: 20 µm.