Vesicles Balance Osmotic Stress with Bending Energy That Can Be Released to Form Daughter Vesicles

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.

Automated summary

The bending energy of the lipid membrane plays a central role in biological processes involving vesicles. By studying the response of single-component giant unilamellar vesicles (GUVs) to external osmotic stress, it is found that the osmotic pressure is balanced by the free energy of membrane bending. After equilibration, the exchange of external glucose solution for pure water leads to rapid formation of monodisperse daughter vesicles inside the GUVs through an endocytosis-like process. The results indicate that the bending energies stored in GUVs are higher than previously thought and have potential consequences for vesicle fusion/fission and osmotic regulation in living cells.