Models of dynamic extraction of lipid tethers from cell membranes

When a ligand that is bound to an integral membrane receptor is pulled, the membrane and the underlying cytoskeleton can deform before either the membrane delaminates from the cytoskeleton or the ligand detaches from the receptor. If the membrane delaminates from the cytoskeleton, it may be further extruded and form a membrane tether. We develop a phenomenological model for this processes by assuming that deformations obey Hooke’s law up to a critical force at which the cell membrane locally detaches from the cytoskeleton and a membrane tether forms. We compute the probability of tether formation and show that they can be extruded only within an intermediate range of force loading rates and pulling velocities. The mean tether length that arises at the moment of ligand detachment is computed as are the force loading rates and pulling velocities that yield the longest tethers.

💡 Research Summary

This paper presents a phenomenological framework for understanding how membrane tethers are generated when a ligand bound to an integral membrane receptor is mechanically pulled. The authors begin by modeling the early deformation of the plasma membrane and its underlying cytoskeleton as a linear elastic system that obeys Hooke’s law. When the applied force reaches a critical threshold (F_c), the membrane locally detaches from the cytoskeleton, initiating the formation of a thin cylindrical tether. After detachment, the tether’s dynamics are governed by the membrane’s bending rigidity, surface tension, and a constant pulling force (f_0) that maintains the tether, consistent with established theories of membrane tube mechanics.

Two loading protocols are considered: (1) a force that increases linearly with time at a loading rate r (pN·s⁻¹), and (2) a constant pulling velocity v (nm·s⁻¹). For each protocol, the probability of membrane‑cytoskeleton detachment (P_det) is derived using a modified Kramers‑type escape model. The escape rate depends on the energy barrier ΔG, temperature T, and the loading rate r, leading to a time‑dependent rate k(t)=k_0 exp