Figure 5.

(A and B) Schematic of forces (A) and a plot of the ring channel radius (B) when the motor protein density is assumed to be constant over time. The ring channel radius r(t) tends to $\beta =\left(f_n{m}_n/k_c{m}_c\right)$ as $t\to \infty$ when $m_c\ne 0$; r₀ refers to the ring channel radius in its reference configuration (Table 1). Greater force exerted normal to the opening results in expansion of the ring channel (light gray dotted and dashed lines), whereas greater force exerted tangential to the opening results in constriction of the ring channel (dark gray dotted and dashed lines). The ring channel can be maintained at a nonzero radius provided there is a balance between tangential and normal forces. The time course plotted here was obtained using Eq. 8 with the parameter values given in Table 1.