ELECTRICAL PROPERTIES OF LIPID BILAYERS

Student: Veronica PRISECARIU

Alexandru Ioan Cuza University of Iași, Faculty of Physics

Introduction Lipid bilayers – generalities Formation of planar bilayers reconstituted Electrical properties Determination of electrical properties Conclusion Bibliography

Summary

The lipid bilayers are the basic structure of cell membrane. Even if they have only a few nanometers in width, they are crucial for the life of cells.

The cell includes the machinery to gather raw materials from the environment, and to construct out of them a new cell in its own image, complete with a new copy of the hereditary information.

Introduction

Generalities

Fig.1. Phospholipids assembled into bilayer structure [1].

• The lipid bilayer is a thin polar membrane made of two layers of lipid molecules;• The most abundant membrane lipids are the phospholipids;• The shape and amphiphilic nature of these molecules cause them to form bilayers

spontaneously in aqueous environments;

Generalities

In aqueous solution, the hydrophobic effect and van der Waals interactions organize and stabilize phospholipids into one of three structures: a micelle, liposome, or bilayer.

Fig. 2. Modes of organization of lipid molecules present in hydrophilic environments [2];

Fig. 3. The process of formation of a membrane in the aperture of Teflon, which separates the two compartments of “BLM cell”. Initially the lipids are deposited on the surface of separation water-air of this two compartments; after the evaporation of solvent and then the successive raising of the aqueous solutions of compartments, in the aperture of membrane is forming the lipid bilayer[4].

Formation of planar bilayers reconstituted

Fig.4. Detailed representation of Teflon aperture which is used as support for the artificial membrane which separates the two compartments of the ‘BLM cell’ [5].

Electrical properties

1. Capacity (C) The capacity is the parameter considered the best tool for probing the stability and integrity of lipid bilayers and for this reason it is measured for every bilayer, even when other properties are the main focus of the measurements.2. Resistance (R)Planar lipid bilayer membranes exhibit resistance in the range of few gigaohms. The resistance is usually calculated in accordance with Ohm’s law as a ratio of voltage applied to (or measured on) the lipid bilayer and current which flows through it.

Cm

Fig.5. The lipid bilayer as capacitor

Determination of electrical properties

Rm CmΔVm

Fig.7. Equivalent circuit of lipid bilayer

Conclusion

The determination of lipid bilayer allow us to characterize an important function of a bilayer: its ability to segregate and prevent the flow of ions in solution, which are important for many applications.

One the most successful commercial application of lipid bilayers has been the use of liposomes for drug delivery, especially for cancer treatment.

[1] H. Lodish et al., Molecular Cell Biology, May 2, 2012;[2] T. Luchian, Electrofiziologie moleculara. Tehnologii si aplicatii, Ed. Sedcom Libris, Iasi, 2006;[3] B. Alberts et al., Molecular biology of the cell, Garland science (USA), 2008;[4] P. Kramar, D. Miklavcic, M. Kotulska, and A. M. Lebar, Advances in Planar Lipid Bilayers and Liposomes, 2010, vol. 11, 30-66;[5] M. Montal, P. Mueller, Formation of Bimolecular Membranes from Lipid Monolayers and a Study of Their Electrical Properties, Proc. Nat. Acad. Sci. USA,Vol. 69, No. 12, pp. 3561-3566, December 1972.

Bibliography

Thank you for your attention!