Figure 5.

Directional water flux, like actin polymerization flux, can drive cell movement. (A) Cells in confined environments can generate water influx at the leading edge and water efflux at the trailing edge. The water flux is connect with directional ionic flows. (B) Fluid flux gives a quantitative kinematic condition for the cell boundary: equation (10). Here v_c is the fluid velocity in the cytoplasm and v₀ is the velocity of the cell leading edge. In time Δt, the new volume element is v₀Δt which is equal to the sum of v_cΔt and J_waterΔt. (C) If the cytoplasm is considered as a 2-phase fluid, the fluid phase only occupies a fraction of the cell volume θ_c. In this case, the new volume is given by a combination of v_c, actin velocity v_n, and J_water and J_actin (equation 11).