The ability of large macromolecules to exhibit non-trivial deviations in colligative properties of their aqueous solutions is well-appreciated in polymer physics. Here, we show that this colligative non-ideality subjects giant lipid vesicles containing macromolecular crowding agents – such as poly(ethylene)glycol, dextran, and their mixtures – to strong osmotic pressure differentials when bathed in small molecule osmolytes, i.e., sucrose or glucose, at comparable concentrations. The resulting osmotically-propelled influx of water across the semi-permeable membrane stretches the membrane boundary activating transient, but damped, pulse-wise oscillations in size, tension, and the spatial organization of membrane components in a cyclical manner <i>en route</i> to equilibration. Mediated by periodic, synchronized pore-formation events, these swell-burst cycles orchestrate pulse-wise ejection of macromolecules from the vesicular interior. Furthermore, these experimental observations are fully corroborated by a theoretical model upon explicitly incorporating the contributions of solution viscosity, solute diffusivity, and colligative non-ideality due to macromolecular crowding in a continuum description, which combines membrane elasticity, continuum transport, and statistical thermodynamics. Our observations recapitulate behaviors of lipid vesicles and red blood cells experiencing sudden osmotic shocks due to large (hundreds of osmolars) differences in the concentrations of small molecule osmolytes and link intravesicular macromolecular crowding with membrane remodeling. They further offer an important insight: Any significant deviation in macromolecular encapsulation, such as spontaneous under- or overcrowding, in single giant vesicles is unlikely, absent specific interactions with membrane lipids, owing to these osmotically generated swell-burst cycles, which acts to null concentration difference across vesicular compartments<b>.</b>

Pulsatile gating of giant vesicles containing macromolecular crowding agents induced by colligative non-ideality

255th National Meeting (2018)

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