The elasticity of uniform, unilamellar vesicles of acidic phospholipids during osmotic swelling is dominated by the ionic strength of the media

Abstract

Uniform, unilamellar vesicles have been prepared by the pH-modification technique. The initial sizes of the vesicles were from 200 to 700 nm and were measured to within 1-3% by photo correlation spectroscopy. Vesicles were made of the dioleoyl esters of phosphatidic acid, phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, the diphytanyl ethers of phosphatidylglycerol, Escherichia coli lipids, and lac permease reconstituted into E. coli lipids. The vesicle suspensions were prepared and then diluted with electrolyte (KCl) and/or nonelectrolyte (sucrose, trehalose, pentaerythritol) impermeants. The amplitude of the swelling is linearly proportional to the osmotic pressure difference across the bilayer. We have determined the elastic modulus, the elastic limit (percent surface expansion at bursting), and the transbilayer pressure difference at bursting for each of these vesicles at constant osmolarity but at different ionic strengths. We find that the elastic properties of the bilayer vary by a factor of 10 in electrolyte media as compared to isosmolal nonelectrolyte media and that this variation appears to be related to both the charge density at the surface and the ionic strength of the media. Anionic lipid vesicles in 150 mM KCl have a significantly higher modulus (50 X 10(7) dyn/cm2) and transbilayer pressure difference (40 mosM) at bursting with a small capacity to stretch (3-4% surface expansion) compared to the same vesicles suspended in nonelectrolyte impermeants. The latter vesicles undergo a significant surface expansion (8-10%), display a low modulus (3 X 10(7) dyn/cm2), and burst at 3-4 mosM bilayer pressure difference. Vesicles suspended in media of constant osmolarity at various ionic strengths display properties with proportional values.(ABSTRACT TRUNCATED AT 250 WORDS)

Stiffening Effect of Cholesterol on Disordered Lipid Phases: A Combined Neutron Spin Echo + Dynamic Light Scattering Analysis of the Bending Elasticity of Large Unilamellar Vesicles

“…Larger fluctuations appear mixed together with translational effects. Dynamic light scattering (DLS) is mainly used to characterize the vesicles with respect to their size and polydispersity but no internal motions are resolved in this case (39)(40)(41)(42). To our knowledge, only a very limited number of works investigate thermal shape fluctuations of vesicles with DLS.…”

Synthesis, Self-Assembling Properties and Incorporation of Carbohydrate-Substituted Porphyrins into Cell Membrane Models

“…[24] Therefore, the rates of rotation and lateral self-diffusion are different, and it has also been shown that the membranes of lipid vesicles formed from PE have large elastic moduli. [25] Swelling of the inverted H II phase causes the interfacial area per molecule to increase. [24] An increased interfacial area will lead to greater binding constants for hydrophobic or amphiphilic compounds.…”

Membrane elasticity effects on permeability measurements in vesicles

“…This linear relationship between area elasticity and membrane tension has been verified for a variety of natural and synthetic lipid bilayers Sun et al, 1986;Li et al, 1986;Evans and Needham, 1987;Haines et al, 1987;Miyamot0 et al, 1988;Duwe and Sackmann, 1990;Rutkowski et al, 1991). From our previous experiments (Bailey et al, 1990), we have shown that shape fluctuations and the resultant repulsive interaction are negligible for small unilamellar vesicles (75-200 nm diameter); hence the linear result is especially appropriate for the model considered here.…”

“…Vesicles are often used as model systems to study solute permeability through bilayers (Lossen, 1972;Selser et al, 1976;Brunner et al, 1980;Carruthers and Melchior, 1983;Castaing et al, 1992), bilayer elasticity (Servuss et al, 1976;Schneider, Jenkins and Webb, 1984;Milon et al, 1986;Sun et al, 1986;Li et al, 1986;Haines et al, 1987;Miyamoto et al, 1988;Duwe and Sackmann, 1990;Rutkowski et al, 1991), and interactions between bilayer membranes (Evans and Needham, 1987;Servuss and Helfrich, 1989;Bailey et al, 1990). In many of these experiments, concentration differences exist between the inside and outside of the vesicle membrane, leading to an osmotic swelling or shrinkage of the vesicles.…”

“…For membranes with relatively low values of K, it should be possible to measure the average swelling of a population of vesicles with quasi-elastic light scattering following an imposed concentration gradient. This has been done for a variety of lipids by several groups to measure K Sun et al, 1986;Li et al, 1986;Haines et al, 1987;Miyamoto et al, 1988;Rutkowski et al, 1991). After K is measured by recording the initial swelling response, the permeability could be measured by following the radius of the vesicles as a function of time.…”