Fig. 1. Increases in traction forces and intracellular Ca²⁺ following the application of stretching forces. Mechanical forces were applied to a migrating NIH3T3 cell by stretching the flexible substratum near the leading edge with a micro needle. Arrows in B and C indicate the direction of stretching. (A-C) Phase contrast and (D-F) traction stress images were recorded prior to (A,D) and following the removal of the needle, at time points indicated (B,C,E,F). Asterisks mark a fiduciary reference point on the substratum (A-C). Traction stress images were rendered with different colors representing the magnitude, from 2.50x10¹ dynes/cm² (violet) to >3.99x10⁴ dynes/cm² (red). To detect the Ca²⁺ concentration, cells loaded with Fluo-4-dextran were recorded before (G,H) or after (I,J) the application of stretching forces. While the cell stretched in control balanced salt solution showed a clear increase in fluorescence intensity 10 minutes after stretching (G,I), the cell stretched in 100 µM Gd³⁺ showed a slight decrease in fluorescence intensity (H,J). Scale bars: 20 µm.