An experimental approach for direct observation of the interaction of polyanions with sphingosine-containing giant vesicles

Giant Unilamellar Vesicle Electroformation: What to Use, What to Avoid, and How to Quantify the Results

Since its inception more than thirty years ago, electroformation has become the most commonly used method for growing giant unilamellar vesicles (GUVs). Although the method seems quite straightforward at first, researchers must consider the interplay of a large number of parameters, different lipid compositions, and internal solutions in order to avoid artifactual results or reproducibility problems. These issues motivated us to write a short review of the most recent methodological developments and possible pitfalls. Additionally, since traditional manual analysis can lead to biased results, we have included a discussion on methods for automatic analysis of GUVs. Finally, we discuss possible improvements in the preparation of GUVs containing high cholesterol contents in order to avoid the formation of artifactual cholesterol crystals. We intend this review to be a reference for those trying to decide what parameters to use as well as an overview providing insight into problems not yet addressed or solved.

Inward multivesiculation at the basal membrane of adherent giant phospholipid vesicles

Adherent giant vesicles composed of phosphatidylcholine, phosphatidylserine and biotinylated lipids form clusters of inward spherical buds at their basal membrane. The process is spontaneous and occurs when the vesicles undergo a sequence of osmotic swelling and deswelling. The daughter vesicles have a uniform size (diameter ≈ 2-3 μm), engulf small volumes of outer fluid and remain attached to the region of the membrane from which they generate, even after restoring the isotonicity. A pinning-sealing mechanism of long-wavelength modes of membrane fluctuations is proposed, by which the just-deflated vesicles reduce the surplus of membrane area and avoid excessive spreading and compression via biotin anchors. The work discusses the rationale behind the mechanism that furnishes GUVs with basal endovesicles, and its prospective use to simulate cellular events or to create molecular carriers.

Efficient electroformation of supergiant unilamellar vesicles containing cationic lipids on ITO-coated electrodes

Giant unilamellar vesicles (GUVs) represent a versatile in vitro system widely used to study properties of lipid membranes and their interaction with biomacromolecules and colloids. Electroformation with indium tin oxide (ITO) coated coverslips as electrodes is a standard approach to GUV production. In the case of cationic GUVs, however, application of this approach leads to notorious difficulties. We discover that this is related to aging of ITO-coated coverslips during their repeated use, which is reflected in their surface topography on the nanoscale. We find that mild annealing of the ITO-coated surface in air reverts the effects of aging and ensures efficient reproducible electroformation of supergiant (diameter > 100 μm) unilamellar vesicles containing cationic lipids.

DNA condensation at freestanding cationic lipid bilayers

We describe a previously unreported coil-globule transition of DNA electrostatically bound to a freestanding fluid cationic lipid membrane. The collapse of a DNA coil into a compact globule takes place after the DNA molecule attaches in an extended conformation to the membrane. DNA condensation is favored at a higher cationic lipid content, while at lower membrane charge densities coexistence of DNA random coils, partially collapsed conformations, and globules is observed.

Electroformation of giant vesicles from an inverse phase precursor

We discuss a simple modification of the well-known method of giant vesicle electroformation that allows for a direct addition of water-soluble species to the phospholipid bilayers. Using this modified method, we prepare phospholipid vesicles decorated with chitosan, a water-soluble polysaccharide currently investigated for potential pharmacological applications. We find that the method allows this polysaccharide with primary amino groups on every glucose subunit to be tightly bound to the membrane, rather than simply being encapsulated.

Population study of sizes and components of self-reproducing giant multilamellar vesicles

Population analysis of a system of self-reproducing giant multilamellar vesicles (GMVs) was carried out by means of flow cytometry. The multidimensional distribution of forward light scattering (FS), side light scattering (SS), and fluorescence (FL) intensities originating from each GMV provided information about changes in a population composed of 104 vesicles. FS-FL dot plots indicated that, after the addition of the membrane precursor, the size distribution of the newly generated vesicles was nearly the same as that of the original, but the catalyst content was reduced. This result can be interpreted as evidence for the occurrence of the self-reproduction of GMVs. Moreover, the new GMVs recovered the amount of catalyst to the initial value, keeping their size distribution constant, when a solution of the catalyst was added to the new GMVs. These results are the first experimental evidence for a novel phenomenon on GMV size distribution during their self-reproducing cycle.

Flexible macromolecules attached to lipid bilayers: impact on fluidity, curvature, permeability and stability of the membranes

This review summarizes recent investigations on the association of macromolecules on lipid bilayers. Hydrophilic and flexible polymers can form soft coronae tenuously adsorbed or anchored on the lipid membrane. Other synthetic macromolecules are embedded in the apolar region of the membrane. Recent experimental and theoretical works focus on the perturbation of lipid properties achieved depending on the nature and strength of binding. Of importance to biomimicry, to tethered model membranes, and drug carriers, the effects achievable include modulation of the lateral diffusivity of lipids, shape distortions, lateral segregations, formation of well-defined nanopores and ultimately the stimuli responsive disruption of the membrane.

Polyelectrolyte-induced peeling of charged multilamellar vesicles

We study mixtures of charged surfactants, which alone in solution form uni- and multilamellar vesicles, and oppositely charged polyelectrolytes (PEs). The phase behavior is investigated at fixed surfactant concentration as a function of the PE-to-surfactant charge ratio, x. We find that, for x > 0, aggregates form. Light microscopy and X-ray scattering experiments show that the isoelectric point plays a crucial role, since the morphology and the microscopic structure of the aggregates are different before (x < or = 1) and after the isoelectric point (x > 1). To better understand the dynamics for the formation of PE/surfactant complexes, we perform light microscopy experiments where we follow in real time the effect of a PE solution on one multilamellar vesicle (MLV). We find that the PE induces a peeling of the bilayers of the MLV one by one. The peeling is accompanied by strong shape fluctuations of the MLV and leads ultimately to a pile of small aggregates. This novel phenomenon is analyzed in detail and discussed in terms of PE-induced tension and pore formation and growth in a surfactant bilayer.