Excess area dependent scaling behavior of nano-sized membrane tethers

TL;DR

This paper introduces a theoretical and experimental framework for estimating the excess membrane area in live cells using tether pulling, revealing universal scaling laws and the importance of wetting region size.

Contribution

The study develops a reliable in silico method to estimate excess membrane area, validated by experiments across multiple cell types, and uncovers universal scaling relationships.

Findings

Tether forces from simulations match experimental data.

All data collapse onto two universal scaling relationships.

Estimated excess area scales linearly with true excess area.

Abstract

Thermal fluctuations in cell membranes manifest as an excess area (${\cal A}_{\rm ex}$) which governs a multitude of physical process at the sub-micron scale. We present a theoretical framework, based on an in silico tether pulling method, which may be used to reliably estimate ${\cal A}_{\rm ex}$ in live cells. The tether forces estimated from our simulations compare well with our experimental measurements for tethers extracted from ruptured GUVs and HeLa cells. We demonstrate the significance and validity of our method by showing that all our calculations along with experiments of tether extraction in 15 different cell types collapse onto two unified scaling relationships mapping tether force, tether radius, bending stiffness $\kappa$, and membrane tension $\sigma$. We show that $R_{\rm bead}$, the size of the wetting region, is an important determinant of the radius of the extracted tether, which is equal to $\xi=\sqrt{\kappa/2\sigma}$ (a characteristic length scale of the membrane) for $R_{\rm bead}<\xi$, and is equal to $R_{\rm bead}$ for $R_{\rm bead}>\xi$. We also find that the estimated excess area follows a linear scaling behavior that only depends on the true value of ${\cal A}_{\rm ex}$ for the membrane, based on which we propose a self-consistent technique to estimate the range of excess membrane areas in a cell.