Biomedical Engineering Reference
In-Depth Information
of
in vivo
electroporation is what cells go through when they are packed in a
tissue (Esser et al. 2007). In some solid tissues the cells may be very tightly
packed but not so much in others, so there are considerable extracellular paths
with conductive medium to allow most of the electric current at low frequency
to flow between the cells. We consider two important effects of the packing of
cells: first, the local transmembrane potential at various parts of each cell's
membrane, which changes considerably with the geometry of the cell, and, sec-
ond, the volumetric ratio of intracellular to extracellular medium. This ratio
is much smaller in tissue than in common
in vitro
setups so there is less effect
of “chemical stress” due to longer periods of open pores. When pores remain
open for a long time and the amount of extracellular medium is relatively
large, concentrations of essential ions may drop below critical levels, while
unwanted molecules may invade the cell in non-negligible quantities, exert-
ing chemical stress on the cell. In a tightly packed tissue on the other hand,
even when the cell's membrane is permeable for a relatively long period of
time and basically uncontrolled exchange occurs freely between the cell and
its surroundings, the cell may still keep its homeostasis because of the limited
amount of extracellular medium in its immediate vicinity.
As for the first effect, Figure 2.4 depicts a schematic diagram of several
cells of various shapes packed together. Some cells in this example are very
close and some have larger extracellular paths between them. The colors on
the cell membranes represent the simulated transmembrane potential due to
FIGURE 2.4
Schematic diagram of packed cells in a solid tissue and the simulated trans-
membrane potential because of a horizontal electric field that is applied exter-
nally. The warm colors represent large transmembrane potentials and cool
colored regions are where the potential is close to zero. The resting potential
is ignored in this case.
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