Fig. 6. Effects of inducing retraction by increasing [Ca²⁺]_i with calcimycin. (A) 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 calcimycin (A) is indicated (arrow), as well as retraction of the rear (R). The addition of calcimycin leads to a rapid increase in calcium indicator fluorescence, to a higher level and of longer duration than the SAC-mediated calcium transients. Traction stress increases slightly at 60 seconds while cell speed decreases. Retraction begins at 80 seconds, as shown by the rapid increase in cell speed and slower cell rounding. (B) IRM observations of a treated keratocyte moving in the direction indicated (arrow) confirm that a brief period of adhesion strengthening occurs at the lateral rear and front edges (black arrowheads) between 0 and 20 seconds after calcimycin addition. The intervening time points are shown as insets. Note the increasing thickness of the line of very close contact, along the cell margin. In this example, retraction starts at the lateral cell edges and continues along the entire cell margin, until completed at 2 minutes.