Abstract
The bending energy of the lipid membrane is central to biological processes involving vesicles, such as endocytosis and exocytosis. To illustrate the role of bending energy in these processes, we study the response of single-component giant unilamellar vesicles (GUVs) subjected to external osmotic stress by glucose addition. For osmotic pressures exceeding 0.15 atm, an abrupt shape change from spherical to prolate occurs, showing that the osmotic pressure is balanced by the free energy of membrane bending. After equilibration, the external glucose solution was exchanged for pure water, yielding rapid formation of monodisperse daughter vesicles inside the GUVs through an endocytosis-like process. Our theoretical analysis shows that this process requires significant free energies stored in the deformed membrane to be kinetically allowed. The results indicate that bending energies stored in GUVs are much higher than previously implicated, with potential consequences for vesicle fusion/fission and the osmotic regulation in living cells.
Highlights
The bending energy of the lipid membrane is central to biological processes involving vesicles, such as endocytosis and exocytosis
The key processes are lipid membrane fusion and fission, typically described as exocytosis and endocytosis when occurring in a cellular environment
One route toward a molecular understanding of exocytosis and endocytosis is to study the fundamental aspects of the phenomenon and to clarify obstacles that must be overcome in specific physiological processes in order to accomplish a specific event
Summary
Where the integral runs over all thermally accessible configurations of the vesicle shell. The answer to Question 2 is that there is a qualitative change in the way that the GUVs accommodate the volume reduction resulting from an increase in osmotic stress To interpret these results in more detail, we follow Seifert[51] and expand the vesicle shape around a spherical shell of radius R0 in terms of the spherical harmonics Ylm pubs.acs.org/JPCL. The upper cutoff lmax in the expansion is determined by the fact that, at length scales comparable to the bilayer thickness, the description of the bilayer as a continuous, elastic surface is no longer relevant Based on this description of shape fluctuations, Zhong-can and Helfrich[32] analyzed the problem of vesicle deformation due to an external pressure.
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