(A) Fourier transform tranction microscopy measurements and the images of a representative A7r5 cell gathered in the measurement process. (a) The single green cell was first identified under fluorescence channel and then the phase-contrast image (upper right) was recorded. Based on beads movement, the traction field was calculated by MATLAB. The magnitude and the direction of the vectors indicate the bead movement, which was used to compute the contractile moment. Scale bar: 50 μm. (b) The color coding for the magnitude of the bead movement. (B) Results of total strain energy measurements (in pJ) of A7r5 cells transfected with phosphomimetic mutants of CaD and EGFP alone (control). The error bars represent the standard errors (SE) of 10 measurements. Single (*) and double (**) asterisks on the peaks denote P < 0.05 and P < 0.005, respectively.