Osmotically induced shape changes of large unilamellar vesicles measured by dynamic light scattering

Static and dynamic light scattering measurements have been used to characte rize the size, size distribution, and shape of extruded vesicles under isot onic conditions. Dynamic light scattering was then used to characterize osm otically induced shape changes by monitoring changes in the hydrodynamic ra dius (Rh) of large unilamellar vesicles (LUVs), These changes are compared to those predicted for several shapes that appear in trajectories through t he phase diagram of the area difference elasticity (ADE) model (Jario et al . 1995. Phys. Rev. E 52:6623-6634). Measurements were performed on dioieoyl phosphatidyicholine (DOPC) vesicles using two membrane-impermeant osmolytes (NaCl and sucrose) and a membrane-permeant osmolyte (urea). For all condit ions, we were able to produce low-polydispersity, nearly spherical vesicles , which are essential for resolving well-defined volume changes and consequ ent shape changes. Hyper-osmotic dilutions of DOPC vesicles in urea produce d no change in Rh, Whereas similar dilutions in NaCl or sucrose caused redu ctions in vesicle volume resulting in observable changes to R-h Under condi tions similar to those of this study, the AIDE model predicts an evolution from spherical to prolate then oblate shapes on increasing volume reduction of LUVs. However, we found that DOPC vesicles became oblate at all applied volume reductions.