Surface Packing of Lipid Bilayers in the Gel State Induced by Osmotic Stress As Measured by the Dimerization of Merocyanine 540

✍ Scribed by J. Arroyo; A.C.Biondi de Lopez; D.L. Bernik; E.A. Disalvo

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 141 KB
• Volume: 203
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1998.5481

✦ Synopsis

vesicles, reduction of the interlamellar space in multilamellar

The differences in the packing of the bilayer interface in lipid liposomes, creation of curvature, and dehydration of the vesicles of different sizes have been measured by determining the membrane phase (5-9).

dimerization equilibrium (K dapp ) of merocyanine 540 (MC540)

A direct consequence produced by the dispersion of vesiincorporated to lipid bilayers. The size was changed by preparing cles in hypertonic media is the volume reduction due to lipid vesicles in isosmotic conditions by extrusion through polycarwater outflux. The decrease in the water volume in the vesibonate membranes of pore size of 100, 200, and 400 nm and by cle lumen can produce a decrease in the particle size altering introducing an osmotic shrinkage with polethylene glycol (PEG).

the spherycal symmetry and producing local changes in

In the absence of osmosis, the packing of dipalmitoylphosphatidylpacking and curvature. However, part of the water extruded choline (DPPC) bilayers decreases with the decrease in the vesicle diameter. In contrast, when the vesicle size is decreased by induc-from the vesicle may be the hydration water around the ing a shrinkage, an increase in the packing of the bilayer interface polar head groups of the phospholipids. In this case, high was observed. A correlation was found between the packing inmolecular weight osmolytes such as PEG can alter the volcrease with the osmotic shock with SUV's and 100, 200, and 400 ume of water distributed around the polar head groups (Wienm LUV's: the larger the vesicle, the larger was the effect of ner and White, 1995). This action may change the memosmosis on the packing. Experiments with vesicles of 100 nm with brane structure at several levels.

the PEG evenly distributed inside and outside showed a 3-fold

Measurements of fluorescence anisotropy with diphenylhigher K dapp . In contrast, the effect on K dapp of ethylene glycol, a hexatriene (DPH) or the oxygen quenching of pyrene in molecule that permeates the bilayer, was shown to be negligible.

DPPC unilamellar vesicles under hypertonic shock have

This suggests that the volume decrease induced by the osmotic

shown no effects of osmosis on the membrane organization shrinkage leads to changes in the lateral packing of the membrane at the region of the hydrocarbon chains throughout the teminterface by effecting the cohesion forces. This effect is comparable to that found when, in the absence of osmosis, the packing in-perature range of 20-47ЊC (4). In contrast, a significant creases with the length of the hydrocarbon chain for a given diameincrease was found in dipalmitoylphosphatidylcholine vesiter. The fact that this conclusion can be derived using a dye that cles subjected to increasing osmolarities when the fluoresdimerizes at the membrane interface allows to conclude that the cence anisotropy was measured with merocyanine 540, a osmotic stress affects the packing by extrusion of the water layers dye that is located at the membrane interface. The magnitude adjacent to polar groups. In contrast, spontaneous curvature can of the surface change and the direction in which it was show defects in the surface packing.