Figure 4.

(a) Forces exerted by a tethered cell on a trapped bead when allowed to rotate slowly forwards (filled symbols, counter-clockwise, + 1/8 Hz) or pushed slowly backwards (open symbols, clockwise, −1/8 Hz). The circles started from the bottom right, where extra points were recorded while the cell was stalled before and after rotations. (b) Forces as in a, recorded with the same cell, only now held directly in the trap without a bead. Note how the cell escaped the trap on several occasions during the backwards push. (c) Mean force vs. speed for this cell with the bead. (d) Mean force vs. speed for this cell without the bead.