Vesicle electrofusion

The phenomenon of membrane electrofusion is of particular interest, because of its widespread use in cell biology and biotechnology (e.g., [162-164] and the references cited therein). The application of electrofusion to cells can lead to the creation of multinucleated viable cells with new properties (this phenomenon is also known as hybridization) (e.g., [164]). In addition, electroporation and electrofusion are often used to introduce molecules like proteins, foreign genes (plasmids), antibodies, and drugs into cells. 

1 Fusing Vesicles with Identical or Different Membrane Composition 

In the later stage of fusion, the neck expansion velocity slows down by more than two orders of magnitude. Here the dynamics is mainly governed by the displacement of the volume of fluid around the fusion neck between the fused vesicles. The restoring force is related to the bending elasticity of the lipid bilayer [36, 37]. 

Fusing two vesicles with membranes of different composition can provide a promising tool for studying raft-like domains in membranes [11,12,133,170,171]. 

---

In this sechon some applicahon aspects of giant vesicle electroporation are considered. In parhcular, it will be demonstrated that creahng macropores in GUVs and observing their closing dynamics can be successfully apphed to the evaluation of material properties of membranes. While in Section 7.4.2 we saw that such experiments can be used to characterize membrane stability in terms of the crihcal porahon potenhal f c, here we will find out how one can also evaluate the edge tension of porated membranes. In addition, another apphcation based on electro-porahon, namely vesicle electrofusion, is introduced whereby the use of GUVs as microreactors suitable for the synthesis of nanoparhcles is demonstrated. 

The physical properhes of hpid bilayers are those that define their response to external perturbations. Knowing the mechanical and rheological characteristics of hpid membranes will prepare us to tackle problems related to stress induced in bilayers by electric fields and the phenomena that it triggers, for example, dynamics of vesicle and cell deformahon, bilayer instability, electroporation, and electrofusion. 

When a DC pulse is applied to a couple of fluid-phase vesicles, which are in contact and oriented in the direction of the field, electrofusion can be observed. Vesicle orientation (and even alignment into pearl chains) can be achieved by application of an AC field to a vesicle suspension. This phenomenon is also observed with cells [164, 165] and is due to dielectric screening of the field. When the suspension is dilute, two vesicles can be brought together via the AC field and aligned. A subsequent application of a DC pulse to such a vesicle couple can lead to fusion. The necessary condition is that poration is induced in the contact area between the two vesicles. The possible steps of the electrofusion of two membranes are schematically illustrated in Figure 7.8a. In Sections 7.5.2.1 and 7.5.2.2, consideration will be given to the fusion of vesicles with different membrane composition or different composition of the enclosed solutions. 

Figure 7.9 Creating a multidomain vesicle by electrofusion of two vesicles with different membrane composition as observed with fluorescence microscopy, (a, b) Images acquired with confocal microscopy scans nearly at the equatorial plane of the fusing vesicles, (a) Vesicle 1 is made of sphingomyelin and cholesterol (7 3) and labeled with one fluorescent dye (green). Vesicle 2 is composed of dioleoylphosphatidylcholine and cholesterol (8 2) and labeled with another...

Figure 26.6 Electroporation of GUV made from C14 (a) and (b) formation of a large pore with pulse durations of 10 ms and 1 ms, respectively (c) and (d) electroadhesion of two vesicles (e) and (f) electrofusion in which diameter increases from 54 to 58 pm (g) and (h) electroexpulsion of an internal vesicle. The scale bar represents 10 pm. In these pictures, the anode is placed at the upper side of the field of view with the cathode at the lower part, and the electric field between the electrodes is 0.5 kV cm . ...

---