Chapter 18. Electroporation and electrofusion of membranes

D.S. Dimitrov
Section on Membrane Structure and Function, National Cancer Institute,
National Institutes of Health, Bethesda, Maryland 20892, USA
and
Central Laboratory of Biophysics,
Bulgarian Academy of Sciences, Sofia 1113, Bulgaria

1. Introductory remarks

1.1. Membrane fusion ensures specific, controlled transfer of molecules in life processes and is important for biotechnology and biomedical research
1.2. Manifestations of cell fusion were observed nearly two centuries ago, while electrofusion was discovered in the late 1970's
1.3. Electric fields can induce fusion of a wide variety of membranes

2.1. Polarization is due to restricted motion of charges
2.2. Interaction of electric fields with polarized membranes induces mechanical stresses
2.3. Forces exerted on polarized membranes can induce structural rearrangements, approach of membranes and their fusion

3.1. High voltage pulses can permeabilize membranes
3.2. The devices for electroporation are conceptually simple
3.3. The transmembrane voltage induced by the external electric fields is accurately described by a simple formula
3.4. Intramembrane field strength is much higher than the strength of the applied electric field
3.5. Membranes are electroporated when the transmembrane voltage exceeds a threshold value
3.6. Transfer of molecules by electroporation is asymmetric
3.7. The threshold voltage of electroporation decreases with an increase in intramembrane mechanical stresses (membrane tension)
3.8. The electromechanical models of electroporation describe membrane rupture as mediated by intramembrane stresses induced by the field
3.9. The energy-based approaches describe formation and expansion of pores as overcoming energy barriers

4.1. Formation of 'pearl chains' of cells in AC fields is due to dielectrophoresis
4.2. The dielectrophoretic force exerted on individual cells can be accurately measured
4.3. The intercellular attraction force increases with decreasing the intermembrane separation and is proportional to the square of the field intensity
4.4. The attraction of cells induced by AC fields can affect fusion efficiency

5.1. Electrofusion is induced at the same threshold voltages as electroporation
5.2. Devices for electrofusion are very similar to those for electroporation
5.3. Long-lived fusogenic states exist after membrane electroporation
5.4. Fusion is localized and results information of intracellular vesicles
5.5. The cell cytoskeleton is reorganized during electrofusion
5.6. Assays based on fluorescence dyes allow accurate measurement of fusion kinetics
5.7. Fusion occurs after a lag time (delay) following the application of the fusogenic trigger
5.8. Delays in electrofusion decrease with an increase in the field strength and are proportional to the solution viscosity
5.9. Rates of fusion can provide information for the time coarse of membrane merging and fusion pore expansion
5.10.Fusion yields and delays are related but may reflect different properties of the fusing membranes

6.1. 'Fusion' of lipid monolayers on liquid surfaces is by diffusion or intermixing driven by surface pressure gradients
6.2. Fusion of bilayers requires overcoming the intramembrane attraction
6.3. The molecular mechanism of bilayer fusion is unknown
6.4. Fusion of cell membranes can be qualitatively described but the molecular rearrangements remain unclear

8. New approaches are needed to understand molecular mechanisms of fusion

Acknowledgement

List of symbols

References