Osmotic Pulsations of Lipid Vesicles under Hypotonic Stress

Abstract

The response of lipid bilayers to osmotic stress is an important part of cellular function. It has been shown that cell-sized giant unilamellar vesicles (GUVs) exposed to hypotonic media, respond to the osmotic assault by undergoing a cyclical sequence of swelling and bursting events, coupled to the membrane's compositional degrees of freedom. In this work, we seek to establish a fundamental and quantitative understanding of the essential pulsatile behavior of GUVs under hypotonic conditions, by advancing a comprehensive theoretical model for vesicle dynamics. We combine experimental and theoretical approaches to characterize the swell-burst cycles of GUVs under hypotonic conditions. We first focus on the membrane rupture mechanism, and show that thermal fluctuations enable stochastic pore nucleations, leading to a dependence of the lytic strain on the load rates. Second, we emphasize the role of solute diffusion in the leak-out process, responsible for the slowdown of the pulsatile dynamics. Finally, we unravel new scaling relationships between the pulsatile dynamics and the GUV properties. Our findings provide a fundamental framework that has the potential to guide future investigations on the non-equilibrium dynamics of vesicles under osmotic stress.