Biomedical Engineering Reference
In-Depth Information
toward a cell to alter its behavior. One prominent method of modifying the
permeability of the membrane is the use of electric fields to create a large
transmembrane potential in a process known as electroporation.
Interactions between electric fields and tissues have been studied for cen-
turies long before the detailed structures of the cell and its membrane were
discovered (Rubinsky 2007). Several studies from the mid-twentieth century
and later (Coster 1965; Sale and Hamilton 1967; Neumann and Rosenheck
1972; Crowley 1973; Lindner et al. 1977; Abidor et al. 1979) began to explore
in a more detailed manner the specific interactions between transmembrane
potential and the membrane's characteristics, such as its permeability and its
mechanical structure. Although we still lack complete knowledge about the
exact mechanism that causes the perceived changes to the membrane under
large electric fields, electroporation is widely regarded today as the process
that is in the heart of the measured phenomena. The explanation is based on
the assumption that a large transmembrane potential causes a physical change
to the mechanical structure of the membrane, creating miniature pores. These
pores may expand in size if the transmembrane potential persists and usually
take one of the two configurations: stable pores, which may stay open even
after the transmembrane potential returns to its normal value at rest, or unsta-
ble pores, which reseal very rapidly when the high electric field is terminated.
Another outcome of electroporation may be the complete disintegration of the
membrane due to numerous pores that have grown so large as to prevent the
membrane from resealing.
When the membrane does not reseal after the application of high electric
field pulses, the process is called
irreversible electroporation,
and one of its
obvious results is that the cell will not be able to survive. It is important to
note that in some cases even cells that managed to reseal their membrane may
ultimately die as a direct result of the electroporation. For example, this may
occur when the membrane was in a high-permeability state for a long time and
the concentration of various ions reached levels that prevented the cell from
recovering. The advantages of tissue ablation using irreversible electroporation
have gained attention recently (Davalos et al. 2005; Esser et al. 2007; Rubinsky
et al. 2007) after years of being considered an unwanted result in the process
of reversible electroporation.
Since its discovery, reversible electroporation has become one of the most
useful lab techniques for introducing proteins, genes, and other molecules
into cells. It is one of the prominent methods used in laboratories today for
transfection, for example, for creating knockout mice.
In vitro
applications of
reversible electroporation are usually carried out by placing a suspension of
cells in a cuvette, a small tube with two metallic plates that act as electrodes.
A voltage is applied to the plates of the cuvette and thus a high-magnitude
electric field is created inside the cuvette, where the cells are found. The
field is relatively uniform with values close to the applied voltage divided by
the distance between the plates. This is a reasonably controlled environment,
and many protocols have been devised over the years for various cell types
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