Figure 5.

Fv relationships when a lamellipodium pushed the bead laterally along the xy direction. (a) Low-resolution image of a lamellipodium near the trapped bead. Scale bar, 2 μm. (b) Micrographs of the lamellipodium pushing the bead laterally during its protrusion. Images were taken at different times during force generation (see c–e). The cross indicates the center of the optical trap. Scale bar, 2 μm. (c–e) The three force components, F_x, F_y, and F_z (gray traces), without filtering and after Gaussian filtering at 0.2 and 1 Hz (green and pink traces, respectively). The dotted box in d indicates the section of the recording used to compute the Fv relationships in f. (f) Fv relationships computed with Gaussian filtering at 0.2 and 1 Hz (green and pink traces, respectively) from a lateral component of the force F_y. Dotted green and pink lines represent −3σ_v at the 0.2- and 1-Hz bandwidths, respectively (where σ_v was calculated from bead fluctuations measured away from the lamellipodia). During the push, F_y becomes negative, and transient retractions are therefore associated with positive velocities. (g) <Fv>_x relationships normalized to F_max from 22 experiments. Data were filtered up to a bandwidth of X Hz. <Fv>_0.2 (green), <Fv>₁ (pink), and <Fv>₁₀ (black).