Figure 1.

Traction force production of individual cellular protrusions exhibit three different regimes: a motor-dominated regime, an intermediate motor-clutch balanced regime, and a clutch-dominated regime. Mean-field motor-clutch model captures force transmission sensitivity to substrate compliance. (A) Sketch of the model and required conditions for the protrusion to operate at each traction force production regime. (B) Dimensionless time-averaged traction force ${\overline{\mathrm{T}}}^{\ast }=\overline{\mathrm{T}}/{\mathrm{n}}_{\mathrm{c}}{\mathrm{F}}_{\mathrm{b}}$ as a function of the dimensionless substrate stiffness $\mathrm{K}$ for various values of the myosin activity parameter $\mathrm{F}$. Protrusions can belong to three different regimes: a motor-dominated regime characterized by the existence of an optimum stiffness for maximal traction that is largely independent of myosin activity ($\mathrm{F}=10$ and $\mathrm{F}=20$), a clutch-dominated regime characterized by stiffness-independent traction forces ($\mathrm{F}=0.25$ and $\mathrm{F}=0.5$), and an intermediate regime characterized by an optimum stiffness sensitive to motor activity ($\mathrm{F}\sim 1$). The three regimes are analyzed in detail in the main text. Solid lines are the numerical solution of the mean-field model Eqs. 3 and 4, and circular solid symbols are the mean statistics obtained from the numerical solution of the stochastic model. There is a very good agreement between the mean-field model solution and stochastic model solution. Parameter values: $\tau =10,\omega =2000$. To see this figure in color, go online.