Figure 2.

Strain rate softening depends on actomyosin binding kinetics. Average axial PK1 stress during first cycle of stress relaxation for cells pretreated with 0.1 nM calyculin (a) to promote myosin activity, untreated (c), or pretreated with 3 $\mu$M Y-27632 (e) to inhibit myosin activity and then subjected stress relaxation at slow (black) or fast (red) strain rates. Calyculin: n = 13 cells slow, 12 cells fast. Untreated: reproduced from Fig. 1f. Y-27632: n = 13 cells slow, 9 cells fast. Normalized peak and decay stress during first cycle of stress relaxation for cells pretreated with calyculin (b), untreated (d), or pretreated with Y-27632 (f). Stresses between cells stretched at the slow versus the fast rate are not significantly different for cells pretreated with calyculin. Solid bars represent mean normalized axial PK1 stress, open circles represent individual measurements. Error bars represent SEM. ^∗p < 0.05. (g) Ratio of stress in cells stretched at fast rate versus slow rate for untreated (black), Y-27632-treated (blue), and calyculin-treated (cyan) cells. Stimulating myosin activity with calyculin decreases strain rate softening, while inhibiting myosin with Y-27632 increases strain rate softening.