Bioelectrochemistry. 2010 Oct;79(2):257-60. Epub 2010 Mar 10.
Electroporation and alternating current cause membrane permeation of
photodynamic cytotoxins yielding necrosis and apoptosis of cancer
Traitcheva N, Berg H.
Institute of Plant Physiology “M. Popov,” Bulgarian Acad. of Sciences, Sofia, Bulgaria.
In order to increase the permeability of cell membranes for low doses
of cytostatic drugs, two bioelectrochemical methods have been compared:
(a) electric pore formation in the plasma membranes by single electric
impulses (electroporation), and (b) reordering of membrane structure by
alternating currents (capacitively coupled). These treatments were
applied to human leukemic K-562 cells and human lymphoma U-937 cells,
yielding apoptotic and necrotic effects, determined by flow cytometry.
Additional cell death occurs after exposure to light irradiation at
wavelengths lambda > 600 nm, of cells which were electroporated and
had incorporated actinomycin-C or daunomycin (daunorubicin). It is
observed that drug uptake after an exponentially decaying
electroporation pulse of the initial field strength Eo=1.4 kV/cm and
pulse time constants in the time range 0.5-3 ms is faster than during
PEMF-treatment, i.e., application of an alternating current of 16 kHz,
voltage U<100 V, I=55 mA, and exposure time 20 min. However, at the
low a.c. voltage of this treatment, more apoptotic and necrotic cells
are produced as compared to the electroporation treatment with one
exponentially decaying voltage pulse. Thus, additional photodynamic
action appears to be more effective than solely drugs and
electroporation as applied in clinical electrochemotherapy, and more
effective than the noninvasive pulsed electromagnetic fields (PEMFs),
for cancer cells in general and animals bearing tumors in particular.
Pol Merkur Lekarski. 2010 Jun;28(168):501-4.
Electroporation and its application.
[Article in Polish]
Sko?ucka N, Saczko J, Kotulska M, Kulbacka J, Choroma?ska A.
Akademia Medyczna we Wroclawiu, Katedra i Zak?ad Biochemii Lekarskiej. email@example.com
Electroporation (EP) is a modern and versatile method that allows the
penetration of macromolecules from the intercellular space into cells
by forming the channels, under the influence of electromagnetic field.
In addition to natural channels and pumps, building cell membranes,
resulting electropores an additional way for the transport of
macromolecules. The use of this phenomenon has brought good results as a
complement to traditional therapeutic methods of treatment during
application of cytostatics. EP combination with chemotherapy has reduced
the need for surgical intervention (rescue authority). Electroporation
is particularly useful for cancer with multidrug resistance, where the
dose that enters the interior of cancer cells is limited.
Electroporation was also used in transfection of nucleic acids, in
photodynamic therapy, cosmetology, as well as the consolidation of the
EEE Trans Biomed Eng. 2009 May;56(5):1491-501. Epub 2009 Feb 6.
A time-dependent numerical model of transmembrane voltage inducement and electroporation of irregularly shaped cells.
Pucihar G, Miklavcic D, Kotnik T.
Faculty of Electrical Engineering, University of Ljubljana, Ljubljana SI-1000, Slovenia. firstname.lastname@example.org
We describe a finite-element model of a realistic irregularly shaped
biological cell in an external electric field that allows the
calculation of time-dependent changes of the induced transmembrane
voltage (Delta Psi) and simulation of cell membrane electroporation. The
model was first tested by comparing its results to the time-dependent
analytical solution for Delta Psi on a nonporated spherical cell, and a
good agreement was obtained. To simulate electroporation, the model was
extended by introducing a variable membrane conductivity. In the regions
exposed to a sufficiently high Delta Psi, the membrane conductivity
rapidly increased with time, leading to a modified spatial distribution
of Delta Psi. We show that steady-state models are insufficient for
accurate description of Delta Psi, as well as determination of
electroporated regions of the membrane, and time-dependent models should
be used instead. Our modeling approach also allows direct comparison of
calculations and experiments. As an example, we show that calculated
regions of electroporation correspond to the regions of molecular
transport observed experimentally on the same cell from which the model
was constructed. Both the time-dependent model of Delta Psi and the
model of electroporation can be exploited further to study the behavior
of more complicated cell systems, including those with cell-to-cell
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi. 2008 Oct;25(5):1206-9.
Research progress of nanosecond pulsed electric field applied to intracellular electromanipulation.
[Article in Chinese]
Yao C, Mo D, Sun C, Chen X, Xiong Z.
Key Lab of High Voltage Engineering and Electrical New Technology,
Ministry of Education, Chongqing University, Chongqing 400044, China. email@example.com
In recent years, many experts have done some researches on experiment
and mechanism of intracellular electromanipulation (IEM) under
nanosecond pulsed electric field (nsPEF). The experiment results have
shown that nsPEF could not induce electroporation of cell membrane, but
could induce intracellular effects such as apoptosis, calcium release,
enhancement of gene expression, and fragmentation of DNA and chromosome.
In order to account for the phenomenon, researchers believe that when
the pulse width of the pulsed electric field is larger than the charging
time of plasma membrane, the pulsed electric field mainly targets on
the outer membrane of cell; and that the effect of the pulsed electric
field on nucleus and nuclear membrane increases with the decrease of the
pulse width. It is also believed that the effect of electroporation
changes from the outer membrane to intracellular electromanipulation
when the pulse width decreases to a value being smaller than the
charging time of plasma membrane.
Biomech Model Mechanobiol. 2008 Oct;7(5):379-86. Epub 2007 Jul 27.
Finite element analysis of microelectrotension of cell membranes.
Bae C, Butler PJ.
Department of Bioengineering, The Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802, USA. firstname.lastname@example.org
Electric fields can be focused by micropipette-based electrodes to
induce stresses on cell membranes leading to tension and poration. To
date, however, these membrane stress distributions have not been
quantified. In this study, we determine membrane tension, stress, and
strain distributions in the vicinity of a microelectrode using finite
element analysis of a multiscale electro-mechanical model of pipette,
media, membrane, actin cortex, and cytoplasm. Electric field forces are
coupled to membranes using the Maxwell stress tensor and membrane
electrocompression theory. Results suggest that micropipette electrodes
provide a new non-contact method to deliver physiological stresses
directly to membranes in a focused and controlled manner, thus providing
the quantitative foundation for micreoelectrotension, a new technique
for membrane mechanobiology.
Ann Biomed Eng. 2007 Jul;35(7):1264-75. Epub 2007 Mar 6.
Electric fields around and within single cells during electroporation-a model study.
Mossop BJ, Barr RC, Henshaw JW, Yuan F.
Department of Biomedical Engineering, Duke University, 136 Hudson Hall, Box 90281, Durham, NC 27708, USA.
One of the key issues in electric field-mediated molecular delivery
into cells is how the intracellular field is altered by electroporation.
Therefore, we simulated the electric field in both the extracellular
and intracellular domains of spherical cells during electroporation. The
electroporated membrane was modeled macroscopically by assuming that
its electric resistivity was smaller than that of the intact membrane.
The size of the electroporated region on the membrane varied from zero
to the entire surface of the cell. We observed that for a range of
values of model constants, the intracellular current could vary several
orders of magnitude whereas the maximum variations in the extracellular
and total currents were less than 8% and 4%, respectively. A similar
difference in the variations was observed when comparing the electric
fields near the center of the cell and across the permeabilized
membrane, respectively. Electroporation also caused redirection of the
extracellular field that was significant only within a small volume in
the vicinity of the permeabilized regions, suggesting that the electric
field can only facilitate passive cellular uptake of charged molecules
near the pores. Within the cell, the field was directed radially from
the permeabilized regions, which may be important for improving
intracellular distribution of charged molecules.
Biophys J. 2008 Jun;94(12):5018-27. Epub 2008 Mar 13.
Quantification of electroporative uptake kinetics and electric field heterogeneity effects in cells.
Kennedy SM, Ji Z, Hedstrom JC, Booske JH, Hagness SC.
Department of Electrical and Computer Engineering, University of Wisconsin, Madison, Wisconsin 53706, USA. email@example.com
We have conducted experiments quantitatively investigating
electroporative uptake kinetics of a fluorescent plasma membrane
integrity indicator, propidium iodide (PI), in HL60 human leukemia cells
resulting from exposure to 40 mus pulsed electric fields (PEFs). These
experiments were possible through the use of calibrated, real-time
fluorescence microscopy and the development of a microcuvette: a
specialized device designed for exposing cell cultures to intense PEFs
while carrying out real-time microscopy. A finite-element electrostatic
simulation was carried out to assess the degree of electric field
heterogeneity between the microcuvette’s electrodes allowing us to
correlate trends in electroporative response to electric field
distribution. Analysis of experimental data identified two distinctive
electroporative uptake signatures: one characterized by low-level,
decelerating uptake beginning immediately after PEF exposure and the
other by high-level, accelerating fluorescence that is manifested
sometimes hundreds of seconds after PEF exposure. The qualitative nature
of these fluorescence signatures was used to isolate the conditions
required to induce exclusively transient electroporation and to discuss
electropore stability and persistence. A range of electric field
strengths resulting in transient electroporation was identified for
HL60s under our experimental conditions existing between 1.6 and 2
kV/cm. Quantitative analysis was used to determine that HL60s
experiencing transient electroporation internalized between 50 and 125
million nucleic acid-bound PI molecules per cell. Finally, we show that
electric field heterogeneity may be used to elicit asymmetric
electroporative PI uptake within cell cultures and within individual
Bioelectrochemistry. 2007 May;70(2):275-82. Epub 2006 Oct 18.
High electrical field effects on cell membranes.
Pliquett U, Joshi RP, Sridhara V, Schoenbach KH.
Frank Reidy Research Center for Bioelectrics 830 Southampton Ave., Suite 5100, Norfolk, VA 23510, United States.
Electrical charging of lipid membranes causes electroporation with
sharp membrane conductance increases. Several recent observations,
especially at very high field strength, are not compatible with the
simple electroporation picture. Here we present several relevant
experiments on cell electrical responses to very high external voltages.
We hypothesize that, not only are aqueous pores created within the
lipid membranes, but that nanoscale membrane fragmentation occurs,
possibly with micelle formation. This effect would produce conductivity
increases beyond simple electroporation and display a relatively fast
turn-off with external voltage. In addition, material loss can be
expected at the anode side of cells, in agreement with published
experimental reports at high fields. Our hypothesis is qualitatively
supported by molecular dynamics simulations. Finally, such cellular
responses might temporarily inactivate voltage-gated and ion-pump
activity, while not necessarily causing cell death. This hypothesis also
supports observations on electrofusion.
J Biomol Struct Dyn. 2007 Apr;24(5):495-503.
Self-electroporation as a model for fusion pore formation.
Luitel P, Schroeter DF, Powell JW.
Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
The creation of a small opening called the fusion pore is a necessary
prerequisite for neurotransmitter release from synaptic vesicles. It is
known that high intensity electric fields can create pores in vesicles
by a process called electroporation. Due to the presence of charged
phosphatidylserine (PS) molecules on the inner leaflet of the cell
membrane, an electric field that is strong enough to cause
electroporation of a synaptic vesicle might be present. It was shown by
K. Rosenheck [K. Rosenheck. Biophys J 75, 1237-1243 (1998)] that in a
planar geometry, fields sufficient to cause electroporation can occur at
intermembrane separations of less than approximately 3 nm. It is
frequently found, however, that the cell membrane is not planar but
caves inward at the locations where a vesicle is close to it.
Indentation of the cell membrane in the fusion region was modelled as a
hemisphere and a theoretical study of the electric field in the vicinity
of the cell membrane taking into account the screening effect of
dissolved ions in the cytoplasm was performed. It was discovered that
fields crossing the electroporation threshold occurred at a distance of 2
nm or less, supporting the claim that electroporation could be a
possible mechanism for fusion pore formation.
IEEE Trans Biomed Eng. 2007 Apr;54(4):611-20.
Hybrid finite element method for describing the electrical response of biological cells to applied fields.
Ying W, Henriquez CS.
Department of Biomedical Engineering, Duke University, Durham, NC 27708-0281, USA. firstname.lastname@example.org
A novel hybrid finite element method (FEM) for modeling the response
of passive and active biological membranes to external stimuli is
presented. The method is based on the differential equations that
describe the conservation of electric flux and membrane currents. By
introducing the electric flux through the cell membrane as an additional
variable, the algorithm decouples the linear partial differential
equation part from the nonlinear ordinary differential equation part
that defines the membrane dynamics of interest. This conveniently
results in two subproblems: a linear interface problem and a nonlinear
initial value problem. The linear interface problem is solved with a
hybrid FEM. The initial value problem is integrated by a standard
ordinary differential equation solver such as the Euler and Runge-Kutta
methods. During time integration, these two subproblems are solved
alternatively. The algorithm can be used to model the interaction of
stimuli with multiple cells of almost arbitrary geometries and complex
ion-channel gating at the plasma membrane. Numerical experiments are
presented demonstrating the uses of the method for modeling field
stimulation and action potential propagation.
Electromagn Biol Med. 2007;26(3):239-50.
Modeling environment for numerical simulation of applied electric fields on biological cells.
Suzuki DO, Ramos A, Marques JL.
Department of Electrical Engineering, Institute of Biomedical
Engineering, Federal University of Santa Catarina (UFSC), Santa
The application of electric pulses in cells increases membrane
permeability. This phenomenon is called electroporation. Current
electroporation models do not explain all experimental findings: part of
this problem is due to the limitations of numerical methods. The
Equivalent Circuit Method (ECM) was developed in an attempt to solve
electromagnetic problems in inhomogeneous and anisotropic media. ECM is
based on modeling of the electrical transport properties of the medium
by lumped circuit elements as capacitance, conductance, and current
sources, representing the displacement, drift, and diffusion current,
respectively. The purpose of the present study was to implement a 2-D
cell Model Development Environment (MDE) of ionic transport process,
local anisotropy around cell membranes, biological interfaces, and the
dispersive behaviour of tissues. We present simulations of a single
cell, skeletal muscle, and polygonal cell arrangement. Simulation of
polygonal form indicates that the potential distribution depends on the
geometrical form of cell. The results demonstrate the importance of the
potential distributions in biological cells to provide strong evidences
for the understanding of electroporation.
Biophys J. 2007 Jan 15;92(2):404-17. Epub 2006 Oct 20.
Modeling electroporation in a single cell.
Krassowska W, Filev PD.
Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA. email@example.com
Electroporation uses electric pulses to promote delivery of DNA and
drugs into cells. This study presents a model of electroporation in a
spherical cell exposed to an electric field. The model determines
transmembrane potential, number of pores, and distribution of pore radii
as functions of time and position on the cell surface. For a 1-ms, 40
kV/m pulse, electroporation consists of three stages: charging of the
cell membrane (0-0.51 micros), creation of pores (0.51-1.43 micros), and
evolution of pore radii (1.43 micros to 1 ms). This pulse creates
approximately 341,000 pores, of which 97.8% are small ( approximately 1
nm radius) and 2.2% are large. The average radius of large pores is 22.8
+/- 18.7 nm, although some pores grow to 419 nm. The highest pore
density occurs on the depolarized and hyperpolarized poles but the
largest pores are on the border of the electroporated regions of the
cell. Despite their much smaller number, large pores comprise 95.3% of
the total pore area and contribute 66% to the increased cell
conductance. For stronger pulses, pore area and cell conductance
increase, but these increases are due to the creation of small pores;
the number and size of large pores do not increase.
Phys Biol. 2006 Nov 2;3(4):233-47.
Nanopore-facilitated, voltage-driven phosphatidylserine translocation in lipid bilayers–in cells and in silico.
Vernier PT, Ziegler MJ, Sun Y, Gundersen MA, Tieleman DP.
Department of Electrical Engineering-Electrophysics, Viterbi School
of Engineering, University of Southern California, Los Angeles CA,
90089-0271, USA. firstname.lastname@example.org
Nanosecond, megavolt-per-meter pulses–higher power but lower total
energy than the electroporative pulses used to introduce normally
excluded material into biological cells–produce large intracellular
electric fields without destructively charging the plasma membrane.
Nanoelectropulse perturbation of mammalian cells causes translocation of
phosphatidylserine (PS) to the outer face of the cell, intracellular
calcium release, and in some cell types a subsequent progression to
apoptosis. Experimental observations and molecular dynamics (MD)
simulations of membranes in pulsed electric fields presented here
support the hypothesis that nanoelectropulse-induced PS externalization
is driven by the electric potential that appears across the lipid
bilayer during a pulse and is facilitated by the poration of the
membrane that occurs even during pulses as brief as 3 ns. MD simulations
of phospholipid bilayers in supraphysiological electric fields show a
tight association between PS externalization and membrane pore formation
on a nanosecond time scale that is consistent with experimental
evidence for electropermeabilization and anode-directed PS translocation
after nanosecond electric pulse exposure, suggesting a molecular
mechanism for nanoelectroporation and nanosecond PS externalization:
electrophoretic migration of the negatively charged PS head group along
the surface of nanometer-diameter electropores initiated by field-driven
alignment of water dipoles at the membrane interface.
BMC Cell Biol. 2006 Oct 19;7:37.
Nanoelectropulse-driven membrane perturbation and small molecule permeabilization.
Vernier PT, Sun Y, Gundersen MA.
Department of Electrical Engineering-Electrophysics, Viterbi School
of Engineering, University of Southern California, Los Angeles, CA
90089-0271, USA. email@example.com
BACKGROUND: Nanosecond, megavolt-per-meter pulsed electric fields
scramble membrane phospholipids, release intracellular calcium, and
induce apoptosis. Flow cytometric and fluorescence microscopy evidence
has associated phospholipid rearrangement directly with nanoelectropulse
exposure and supports the hypothesis that the potential that develops
across the lipid bilayer during an electric pulse drives
phosphatidylserine (PS) externalization.
RESULTS: In this work we extend observations of cells exposed to
electric pulses with 30 ns and 7 ns durations to still narrower pulse
widths, and we find that even 3 ns pulses are sufficient to produce
responses similar to those reported previously. We show here that in
contrast to unipolar pulses, which perturb membrane phospholipid order,
tracked with FM1-43 fluorescence, only at the anode side of the cell,
bipolar pulses redistribute phospholipids at both the anode and cathode
poles, consistent with migration of the anionic PS head group in the
transmembrane field. In addition, we demonstrate that, as predicted by
the membrane charging hypothesis, a train of shorter pulses requires
higher fields to produce phospholipid scrambling comparable to that
produced by a time-equivalent train of longer pulses (for a given
applied field, 30, 4 ns pulses produce a weaker response than 4, 30 ns
pulses). Finally, we show that influx of YO-PRO-1, a fluorescent dye
used to detect early apoptosis and activation of the purinergic P2X7
receptor channels, is observed after exposure of Jurkat T lymphoblasts
to sufficiently large numbers of pulses, suggesting that membrane
poration occurs even with nanosecond pulses when the electric field is
high enough. Propidium iodide entry, a traditional indicator of
electroporation, occurs with even higher pulse counts.
CONCLUSION: Megavolt-per-meter electric pulses as short as 3 ns alter
the structure of the plasma membrane and permeabilize the cell to small
molecules. The dose responses of cells to unipolar and bipolar pulses
ranging from 3 ns to 30 ns duration support the hypothesis that a
field-driven charging of the membrane dielectric causes the formation of
pores on a nanosecond time scale, and that the anionic phospholipid PS
migrates electrophoretically along the wall of these pores to the
external face of the membrane.
IEEE Trans Nanobioscience. 2006 Sep;5(3):157-63.
Effect of pore size on the calculated pressure at biological cells pore wall.
El-Hag AH, Zheng Z, Boggs SA, Jayaram SH.
Electrical Engineering Department, American University of Sharjah, Sharjah, United Arab Emirate. firstname.lastname@example.org
A transient nonlinear finite-element program has been used to
calculate the electric field distribution as a function of time for a
spherical cell with a pore in a conducting medium during application of a
subnanosecond rise time “step” wave, including the effects of dipolar
saturation in the water-based cytoplasm and cell medium. The
time-dependent pressure on the pore wall has been computed as a function
of time as the system polarizes from the change of the energy in the
electric field to the left (inside the pore) and to the right (inside
the membrane) of the pore wall. The computations suggest that dipolar
saturation, while significant, has little effect on the time-dependent
electric field distribution but a substantial effect on the
field-induced pore wall pressure. Also, the effect of pore size on both
the computed electric field and field-induced pressure was studied. As
the pore size increases, a collapse in both the electric field and
field-induced pressure has been noticed. This suggests that as the pore
size increases, the driving force for further opening the pore is not
Phys Rev E Stat Nonlin Soft Matter Phys. 2006 Aug;74(2 Pt 1):021904. Epub 2006 Aug 3.
Membrane electroporation: The absolute rate equation and nanosecond time scale pore creation.
Vasilkoski Z, Esser AT, Gowrishankar TR, Weaver JC.
Harvard-MIT Division of Health Sciences and Technology, Massachusetts
Institute of Technology, Cambridge, Massachusetts 02139, USA.
The recent applications of nanosecond, megavolt-per-meter electric
field pulses to biological systems show striking cellular and
subcellular electric field induced effects and revive the interest in
the biophysical mechanism of electroporation. We first show that the
absolute rate theory, with experimentally based parameter input, is
consistent with membrane pore creation on a nanosecond time scale.
Secondly we use a Smoluchowski equation-based model to formulate a
self-consistent theoretical approach. The analysis is carried out for a
planar cell membrane patch exposed to a 10 ns trapezoidal pulse with 1.5
ns rise and fall times. Results demonstrate reversible
supraelectroporation behavior in terms of transmembrane voltage, pore
density, membrane conductance, fractional aqueous area, pore
distribution, and average pore radius. We further motivate and justify
the use of Krassowska’s asymptotic electroporation model for analyzing
nanosecond pulses, showing that pore creation dominates the electrical
response and that pore expansion is a negligible effect on this time
J Biomech Eng. 2006 Feb;128(1):76-84.
Numerical modeling of in vivo plate electroporation thermal dose assessment.
Becker SM, Kuznetsov AV.
Mechanical and Aerospace Engineering, North Carolina State University, Box 7910, Raleigh, NC 27695, USA. email@example.com
Electroporation is an approach used to enhance the transport of large
molecules to the cell cytosol in which a targeted tissue region is
exposed to a series of electric pulses. The cell membrane, which
normally acts as a barrier to large molecule transport into the cell
interior, is temporarily destabilized due to the development of pores in
the cell membrane. Consequently, agents that are ordinarily unable
enter the cell are able to pass through the cell membrane. Of possible
concern when exposing biological tissue to an electric field is thermal
tissue damage associated with joule heating. This paper explores the
thermal effects of various geometric, biological, and electroporation
pulse parameters including the blood vessel presence and size, plate
electrode configuration, and pulse duration and frequency. A
three-dimensional transient finite volume model of in vivo parallel
plate electroporation of liver tissue is used to develop a better
understanding of the underlying relationships between the physical
parameters involved with tissue electroporation and resulting thermal
Conf Proc IEEE Eng Med Biol Soc. 2006;1:2276-9.
Field stimulation of cells in suspension: use of a hybrid finite element method.
Ying W, Pourtaheri N, Henriquez CS.
Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA. firstname.lastname@example.org
Electric fields are used in a range of applications, including gene
transfection, electrochemotherapy of tumors and cardiac defibrillation.
Despite the widespread use of electric fields, most of the theoretical
and computational studies on discrete cellular tissue have focused on a
single cell. In this work, we propose a hybrid finite element method to
simulate the effects of external electric fields on clusters of
excitable cells. The method can be used to model cells of arbitrary cell
geometries and non-linear membrane dynamics. The results show that the
response of multiple cell, like a single cell, is a two-stage process
consisting of the initial polarization that proceeds with cellular time
constant (less than one microsecond) and the actual excitation of the
cell membrane that proceeds with the membrane time constant (on the
order of milliseconds). The results also show that the stimulation of a
given cell depends in part on the arrangement of cells within the field
and not simply the location within the field, suggesting that classical
approaches that ignores the effect of the cells on the field do not
adequately predict the cellular response.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Sep;72(3 Pt 1):031902. Epub 2005 Sep 8.
Simulations of nanopore formation and phosphatidylserine
externalization in lipid membranes subjected to a high-intensity,
ultrashort electric pulse.
Hu Q, Joshi RP, Schoenbach KH.
Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529-0246, USA.
A combined MD simulator and time dependent Laplace solver are used to
analyze the electrically driven phosphatidylserine externalization
process in cells. Time dependent details of nanopore formation at cell
membranes in response to a high-intensity (100 kV/cm), ultrashort (10
ns) electric pulse are also probed. Our results show that nanosized
pores could typically be formed within about 5 ns. These predictions are
in very good agreement with recent experimental data. It is also
demonstrated that defect formation and PS externalization in membranes
should begin on the anode side. Finally, the simulations confirm that PS
externalization is a nanopore facilitated event, rather than the result
of molecular translocation across the trans-membrane energy barrier.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Mar;71(3 Pt 1):031914. Epub 2005 Mar 29.
Simulations of transient membrane behavior in cells subjected to a high-intensity ultrashort electric pulse.
Hu Q, Viswanadham S, Joshi RP, Schoenbach KH, Beebe SJ, Blackmore PF.
Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529-0246, USA.
A molecular dynamics (MD) scheme is combined with a distributed
circuit model for a self-consistent analysis of the transient membrane
response for cells subjected to an ultrashort (nanosecond)
high-intensity (approximately 0.01-V/nm spatially averaged field)
voltage pulse. The dynamical, stochastic, many-body aspects are treated
at the molecular level by resorting to a course-grained representation
of the membrane lipid molecules. Coupling the Smoluchowski equation to
the distributed electrical model for current flow provides the
time-dependent transmembrane fields for the MD simulations. A good match
between the simulation results and available experimental data is
obtained. Predictions include pore formation times of about 5-6 ns. It
is also shown that the pore formation process would tend to begin from
the anodic side of an electrically stressed membrane. Furthermore, the
present simulations demonstrate that ions could facilitate pore
formation. This could be of practical importance and have direct
relevance to the recent observations of calcium release from the
endoplasmic reticulum in cells subjected to such ultrashort,
Bioelectromagnetics. 2004 Dec;25(8):634-7.
Electroporation of a lipid bilayer as a chemical reaction.
Bier M, Gowrishankar TR, Chen W, Lee RC.
Department of Physics, East Carolina University, Greenville, North Carolina 27858, USA. email@example.com
When a cell’s transmembrane potential is increased from a
physiological one to more than 370 mV, the transmembrane current
increases more than hundredfold within a millisecond. This is due to the
formation of conductive pores in the membrane. We construct a model in
which we conceive of pore formation as a voltage sensitive chemical
reaction. The model predicts the logarithm of the pore formation rate to
increase proportionally to the square of the voltage. We measure
currents through frog muscle cell membranes under 8 ms pulses of up to
440 mV. The experimental data appear consistent with the model.
IEEE Trans Nanobioscience. 2004 Sep;3(3):225-31.
Electric fields within cells as a function of membrane resistivity–a model study.
Mossop BJ, Barr RC, Zaharoff DA, Yuan F.
Department of Biomedical Engineering, Duke University, Durham, NC 27708-0281, USA.
Externally applied electric fields play an important role in many
therapeutic modalities, but the fields they produce inside cells remain
largely unknown. This study makes use of a three-dimensional model to
determine the electric field that exists in the intracellular domain of a
10-microm spherical cell exposed to an applied field of 100 V/cm. The
transmembrane potential resulting from the applied field was also
determined and its change was compared to those of the intracellular
field. The intracellular field increased as the membrane resistance
decreased over a wide range of values. The results showed that the
intracellular electric field was about 1.1 mV/cm for Rm of 10,000 omega x
cm2, increasing to about 111 mV/cm as Rm decreased to 100 omega x cm2.
Over this range of Rm the transmembrane potential was nearly constant.
The transmembrane potential declined only as Rm decreased below 1 omega x
cm2. The simulation results suggest that intracellular electric field
depends on Rm in its physiologic range, and may not be negligible in
understanding some mechanisms of electric field-mediated therapies.
FEBS Lett. 2004 Aug 13;572(1-3):103-8.
Nanosecond pulsed electric fields perturb membrane phospholipids in T lymphoblasts.
Vernier PT, Sun Y, Marcu L, Craft CM, Gundersen MA.
Department of Materials Science, School of Engineering, University of Southern California, Los Angeles, CA 90089-0271, USA. firstname.lastname@example.org
Nanosecond, megavolt-per-meter pulsed electric fields scramble the
asymmetric arrangement of phospholipids in cell membranes without the
permeabilization associated with longer, lower-field pulses. A single 30
ns, 2.5 MV/m pulse produces perturbations consistent with
phosphatidylserine (PS) externalization in Jurkat T lymphoblasts within
milliseconds, polarized in the direction of the applied field,
indicating an immediate interaction between membrane components and the
electric field. This disturbance occurs only at the anode pole of the
cell, supporting the hypothesis that the pulsed field drives the
negatively charged PS head group toward the positive electrode, directly
providing the energy for crossing the membrane dielectric barrier.
Bioelectrochemistry. 2004 Jun;63(1-2):311-5.
The effect of resting transmembrane voltage on cell electropermeabilization: a numerical analysis.
Valic B, Pavlin M, Miklavcic D.
Faculty of Electrical Engineering, University of Ljubljana, Trzaska 25, SI-1000 Ljubljana, Slovenia.
The transmembrane voltage induced due to applied electric field
superimposes to the resting transmembrane voltage of the cell. On the
part of the cell membrane, where the transmembrane voltage exceeds the
threshold transmembrane voltage, changes in the membrane occur, leading
to increase in membrane permeability known as electropermeabilization.
This part of the cell membrane represents the permeabilized area through
which the transport of molecules occurs. In this paper we calculated
numerically the permeabilized area for different electric field
strength, resting transmembrane voltage, cell shape and cell orientation
with respect to the applied electric field. Results show that when the
transmembrane voltage is near the threshold transmembrane voltage, the
permeabilized area of the cell is increased on the anodic side and
decreased on the cathodic side due to the resting transmembrane voltage.
In some cases, only anodic side of the cell is permeabilized.
Therefore, by using bipolar pulses, the permeabilized area can be
significantly increased and consequentially also the efficiency of
electropermeabilization. However, when the induced transmembrane voltage
is far above the threshold, the effect of the resting transmembrane
voltage is negligible. These observations are valid for different cell
shapes and orientations.
Biophys J. 2004 Jun;86(6):4040-8.
Nanoelectropulse-induced phosphatidylserine translocation.
Vernier PT, Sun Y, Marcu L, Craft CM, Gundersen MA.
Department of Electrical Engineering-Electrophysics, School of
Engineering, MOSIS, University of Southern California, Los Angeles,
California, USA. email@example.com
Nanosecond, megavolt-per-meter, pulsed electric fields induce
phosphatidylserine (PS) externalization, intracellular calcium
redistribution, and apoptosis in Jurkat T-lymphoblasts, without causing
immediately apparent physical damage to the cells. Intracellular calcium
mobilization occurs within milliseconds of pulse exposure, and membrane
phospholipid translocation is observed within minutes. Pulsed cells
maintain cytoplasmic membrane integrity, blocking propidium iodide and
Trypan blue. Indicators of apoptosis-caspase activation and loss of
mitochondrial membrane potential-appear in nanoelectropulsed cells at
later times. Although a theoretical framework has been established,
specific mechanisms through which external nanosecond pulsed electric
fields trigger intracellular responses in actively growing cells have
not yet been experimentally characterized. This report focuses on the
membrane phospholipid rearrangement that appears after ultrashort pulse
exposure. We present evidence that the minimum field strength required
for PS externalization in actively metabolizing Jurkat cells with 7-ns
pulses produces transmembrane potentials associated with increased
membrane conductance when pulse widths are microseconds rather than
nanoseconds. We also show that nanoelectropulse trains delivered at
repetition rates from 2 to 2000 Hz have similar effects, that
nanoelectropulse-induced PS externalization does not require calcium in
the external medium, and that the pulse regimens used in these
experiments do not cause significant intra- or extracellular Joule
Phys Rev E Stat Nonlin Soft Matter Phys. 2004 Apr;69(4 Pt 1):041901. Epub 2004 Apr 14.
Fields and forces acting on a planar membrane with a conducting channel.
Bivas I, Danelon C.
Laboratory of Liquid Crystals, Institute of Solid State Physics,
Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Boulevard, Sofia
1784, Bulgaria. firstname.lastname@example.org
Modeling electric fields and forces around a channel in a planar
membrane is still an open problem. Until now, most of the existing
theories have oversimplified the electric field distribution by placing
the electrode directly at the entry of the channel. However, in any
relevant experimental setup the electrodes are placed far away in the
electrolyte solution. We demonstrate that long-range deformation of the
electric field distribution appears around the membrane, spanning on
distances of the order of the distance between the membrane and the
electrode. The forces acting due to this distribution are in most of the
cases negligible. They can be important for channels with radii of the
order of the thickness of the layer of structured water at the oil-water
Bioelectrochemistry. 2003 Oct;61(1-2):65-72.
Sub-microsecond, intense pulsed electric field applications to cells show specificity of effects.
Hair PS, Schoenbach KH, Buescher ES.
Center for Pediatric Research, Eastern Virginia Medical School, Norfolk, VA 23510, USA.
Application of sub-microsecond duration (60-300 ns), intense (15-60
kV/cm) pulsed electric fields (sm/i-PEF) to six types of human cells was
examined for its effects on individual cell surface membrane
permeability and membrane potential. With short (60 ns) pulses,
increasing percentages of Jurkat cells showed propidium iodide (PI)
uptake at progressively shorter post-pulse times as the pulse train
increased from 1 to 10 sequential pulses, while human blood
polymorphonuclear leukocytes (PMN) were unresponsive to these short
pulses regardless of train size. With 300 ns pulses, a similar pattern
(increasing percentages of cells taking up PI, and progressively shorter
times of onset after pulse applications as pulse train size increased)
was seen with both Jurkat cells and PMN, but the patterns for both
effects were different. Jurkat cell size did not appear to influence the
responsiveness of this cell type. Comparisons of sm/i-PEF-induced PI
uptake by human monocyte-derived macrophages vs. aged human mononuclear
cells, human trunk skin (HTS) cells vs. fresh human mononuclear cells
and human macrophages vs. HTS cells showed similar overall effects, but
with differences between the patterns for each cell type compared
(except the macrophages vs. HTS cells comparison). Application of
sm/i-PEFs also caused different patterns of membrane potential loss in
Jurkat cells vs. PMN. Jurkat cells developed significant decreases in t
heir membrane potential only following the highest intensity pulse
applications examined, i.e., 300 ns, 60 kV/cm x5, while PMN showed this
effect over the entire range of pulse intensities (300 ns, 15-60 kV/cm,
x5) applied. These data indicate that sm/i-PEF applications can have
“specificity” (i.e., achieve different levels of effect in different
cell types), that cell size does not appear to be the major factor
determining sm/i-PEF effects in either Jurkat cells or PMN, that
heterogeneous sm/i-PEF effects on cells tend to become homogeneous with
increasing pulse train size, and that specificity of sm/i-PEF
applications effects can occur at either end of the sm/i-PEF intensity
Eur Biophys J. 2003 Sep;32(6):519-28. Epub 2003 Apr 24.
Effect of electric field induced transmembrane potential on spheroidal cells: theory and experiment.
Valic B, Golzio M, Pavlin M, Schatz A, Faurie C, Gabriel B, Teissié J, Rols MP, Miklavcic D.
Faculty of Electrical Engineering, University of Ljubljana, Trzaska 25, 1000 Ljubljana, Slovenia.
The transmembrane potential on a cell exposed to an electric field is
a critical parameter for successful cell permeabilization. In this
study, the effect of cell shape and orientation on the induced
transmembrane potential was analyzed. The transmembrane potential was
calculated on prolate and oblate spheroidal cells for various
orientations with respect to the electric field direction, both
numerically and analytically. Changing the orientation of the cells
decreases the induced transmembrane potential from its maximum value
when the longest axis of the cell is parallel to the electric field, to
its minimum value when the longest axis of the cell is perpendicular to
the electric field. The dependency on orientation is more pronounced for
elongated cells while it is negligible for spherical cells. The part of
the cell membrane where a threshold transmembrane potential is exceeded
represents the area of electropermeabilization, i.e. the membrane area
through which the transport of molecules is established. Therefore the
surface exposed to the transmembrane potential above the threshold value
was calculated. The biological relevance of these theoretical results
was confirmed with experimental results of the electropermeabilization
of plated Chinese hamster ovary cells, which are elongated. Theoretical
and experimental results show that permeabilization is not only a
function of electric field intensity and cell size but also of cell
shape and orientation.
Biophys J. 2003 Aug;85(2):719-29.
Effective conductivity of a suspension of permeabilized cells: a theoretical analysis.
Pavlin M, Miklavcic D.
University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia. email@example.com
During the electroporation cell membrane undergoes structural
changes, which increase the membrane conductivity and consequently lead
to a change in effective conductivity of a cell suspension. To correlate
microscopic membrane changes to macroscopic changes in conductivity of a
suspension, we analyzed the effective conductivity theoretically, using
two different approaches: numerically, using the finite elements
method; and analytically, by using the equivalence principle. We derived
the equation, which connects membrane conductivity with effective
conductivity of the cell suspension. The changes in effective
conductivity were analyzed for different parameters: cell volume
fraction, membrane and medium conductivity, critical transmembrane
potential, and cell orientation. In our analysis we used a tensor form
of the effective conductivity, thus taking into account the anisotropic
nature of the cell electropermeabilization and rotation of the cells. To
determine the effect of cell rotation, as questioned by some authors,
the difference between conductivity of a cell suspension with normally
distributed orientations and parallel orientation was also calculated,
and determined to be <10%. The presented theory provides a
theoretical basis for the analysis of measurements of the effective
conductivity during electroporation.
Adv Anat Embryol Cell Biol. 2003;173:III-IX, 1-77.
Electric field-induced effects on neuronal cell biology accompanying dielectrophoretic trapping.
University of Twente, Faculty of Electrical Engineering, Mathematics
and Computer Science, Laboratory of Measurement and Instrumentation,
Laboratory of Biomedical Engineering, P.O. Box 217, 7500 AE Enschede,
The Netherlands. firstname.lastname@example.org
Trapping neuronal cells may aid in the creation of the cultured
neuron probe. The aim of the development of this probe is the creation
of the interface between neuronal cells or tissue in a (human) body and
electrodes that can be used to stimulate nerves in the body by an
external electrical signal in a very selective way. In this way,
functions that were (partially) lost due to nervous system injury or
disease may be restored. First, a direct contact between cultured
neurons and electrodes is created. This is realized using a
microelectrode array (MEA) which can be fabricated using standard
photolithographic and etching methods. Section 1 gives an overview of
the human nervous system, methods for functional recovery focused on the
cultured neuron probe, and the prerequisites for culturing neurons on a
microelectrode array. An important aspect in the selective stimulation
of neuronal cells is the positioning of cells or a small group of cells
on top of each of the electrode sites of the MEA. One of the most
efficient methods for trapping neuronal cells is to make use of
di-electrophoresis (DEP). Dielectrophoretic forces are created when
(polarizable) cells are located in nonuniform electric fields. Depending
on the electrical properties of the cells and the suspending medium,
the DEP force directs the cells towards the regions of high field
strength (positive dielectrophoresis; PDEP) or towards regions of
minimal field intensities (negative dielectrophoresis; NDEP). Since
neurons require a physiological medium with a sufficient concentration
of Na+, the medium conductivity is rather high (~ 1.6 S/m). The result
is that negative dielectrophoretic forces are created over the entire
frequency range. With the use of a planar quadrupole electrode sturcture
negative forces are directed so that in the center of this structure
cell can be collected. The process of trapping cortical rat neurons is
described in Sect. 2 theoretically and experimentally. Medium and cell
properties are frequency-dependent due to relaxation processes, which
have a direct influence on the strength of the dielectrophorectic force.
On the other hand, the nonideal material properties of the gold
electrodes and glass substrate largely determine the electric field
strength created inside the medium. Especially, the electrode-medium
interface results in a significant loss of the imput signal at lower
frequencies (< 1 MHz), and thus a reduction of the electric field
strength inside the medium. Furthermore, due to the high medium
conductivity, the electric field causes Joule heating. Local temperature
rises result in local gradients in fluid density, which induces fluid
flow. The electrode-medium interface and induced fluid flow are
theoretically investigated with the use of modeling techniques such as
finite elements modeling. Experimental and theoretical results agreed
with each other on the occurrence of the effects described in this
section. For the creation of the cultured neuron probe, preservation of
cell viability during the trapping process is a prerequisite. Cell
viability of dielectrophoretically trapped neurons has to be
investigated. The membrane potential induced by the external field plays
a crucial role in preservation of cell viability. The membrane can
effectively be represented by a capaticance in parallel woth a low
conductance; with increasing frequency and /or decreasing field strength
the induced membrane potential decreases. At high induced membrane
potentials ths representation for the membrane is no longer valid. At
this point membrane breakdown occurs and the normally insulating
membrane becomes conductive and permeable. The creation of electropores
has been proposed in literature to be the cause of this high
permeability state. Pores may grow or many small pores may be created
which eventually may lead to membrane rupture, and thus cell death.
Membrane breakdown may be reversible, but a chemical imbalance created
during the high permeability state may still exist after the resealing
of the membrane. This may cause cell death after several hours or even
days after field application. Section 3 gives a detailed description of
membrane breakdown. Since many investigations on electroporation of
lipid bilayers and cell membranes are based on uniform electric fields, a
finite element model is used to investigate induced membrane potentials
in the nonuniform field created by the quadropole electrode structure.
Modeling results are presented in cmbination with the results of
breakdown experiments using four frequencies in the range from 100 kHz
to 1MHz. Radomly positioned neuronals cells were exposed to stepwise
increasing electric field strengths. The field strength at which
membrane rupture occurred gives an indication of the maximum induced
membrane potential. Due to the nonuniformity of the electric field, cell
collapse was expected to be position-dependent. However, at 100 kHz
cells collapsed at a break down level of about 0.4 V, in
contradistinction to findings at higher frequencies where more variation
in breakdown levels were found. Model simulations were able to explain
the experimental results. For examining whether the neuronal cells
trapped by dielectrophoresis were still viable after the trapping
process, the frequency range was divided into two ranges. First, a high
frequency (14 MHz) and a rather low signal amplitude (3 Vpp) were used
to trap cells. At this high frequency the field-induced membrane
potential is small according to the theoretical model, and therefore no
real damage is expected. The experimental analysis included the
investigation of the growth of the neurons, number and length of the
processes (dendrites and axons), and the number of outgrowing (~ viable)
versus nonoutgrowing (~ nonviable) neural cells. The experimental
results agreed with the expectation. The effect of the use of driving
signals with lower frequencies and/or higher amplitudes on cell
viability was investigated using a staining method as described in the
second part of Sect. 4. Survival chances are not directly linked to the
estimated maximum induced membrane potential. The frequency of the dield
plays an important role, decreasing frequency lowering the chance of
survival. A lower frequency limit of 100 kHz is preferable at field
strengths less than 80 k V/m, while with increasing field strength this
limit shifts towards higher frequencies. The theoretical and
experimental results presented in this review form the inception of the
development of new electrode structures for trapping neuronal cells on
top of each of the electrodes of the MEA. New ways to investigate cell
properties and the phenomenon of electroporation using electrokinetic
methods were developed that can be exploited in future research linking
cell biology to technology.
IEEE Trans Biomed Eng. 2002 Oct;49(10):1195-203.
Investigating membrane breakdown of neuronal cells exposed to
nonuniform electric fields by finite-element modeling and experiments.
Heida T, Wagenaar JB, Rutten WL, Marani E.
Institute of BioMedical Technology, Department of Biomedical
Engineering, Faculty of Electrical Engineering, University of Twente,
Enschede, The Netherlands.
High electric field strengths may induce high cell membrane
potentials. At a certain breakdown level the membrane potential becomes
constant due to the transition from an insulating state into a high
conductivity and high permeability state. Pores are thought to be
created through which molecules may be transported into and out of the
cell interior. Membrane rupture may follow due to the expansion of pores
or the creation of many small pores across a certain part of the
membrane surface. In nonuniform electric fields, it is difficult to
predict the electroporated membrane area. Therefore, in this study the
induced membrane potential and the membrane area where this potential
exceeds the breakdown level is investigated by finite-element modeling.
Results from experiments in which the collapse of neuronal cells was
detected were combined with the computed field strengths in order to
investigate membrane breakdown and membrane rupture. It was found that
in nonuniform fields membrane rupture is position dependent, especially
at higher breakdown levels. This indicates that the size of the membrane
site that is affected by electroporation determines rupture.
Phys Med Biol. 2000 Jul;45(7):1965-88.
Nonlinear cell response to strong electric fields.
Bardos DC, Thompson CJ, Yang YS, Joyner KH.
Department of Mathematics and Statistics, University of Melbourne, Parkville, Victoria , Australia.
The response of living cells to externally applied electric fields is
of widespread interest. In particular, the intensification of electric
fields across cell membranes is believed to be responsible, through
membrane rupture and reversible membrane breakdown processes, for
certain types of tissue damage in electrical trauma cases which cannot
be attributed to Joule heating. Large elongated cells such as skeletal
muscle fibres are particularly vulnerable to such damage. Previous
theoretical studies of field intensification across cell membranes in
such cells have assumed the membrane current to be linear in the applied
field (Ohmic membrane conductivity) and were limited to sinusoidal
applied fields. In this paper, we investigate a simple model of a long
cylindrical cell, corresponding to nerve or skeletal muscle cells.
Employing the electroquasistatic approximation, a system of coupled
first-order differential equations for the membrane electric field is
derived which incorporates arbitrary time dependence in the external
field and nonlinear membrane response (non-Ohmic conductivity). The
behaviour of this model is investigated for a variety of applied fields
in both the linear and highly nonlinear regimes. We find that peak
membrane fields predicted by the nonlinear model are approximately twice
as intense, for low-frequency electrical trauma conditions, as those of
the linear theory.
IEEE Trans Biomed Eng. 2002 Jun;49(6):605-12.
Dependence of induced transmembrane potential on cell density, arrangement, and cell position inside a cell system.
Pavlin M, Pavselj N, Miklavcic D.
University of Ljubljana, Faculty of Electrical Engineering, Slovenia.
A nonuniform transmembrane potential (TMP) is induced on a cell
membrane exposed to external electric field. If the induced TMP is above
the threshold value, cell membrane becomes permeabilized in a
reversible process called electropermeabilization. Studying electric
potential distribution on the cell membrane gives us an insight into the
effects of the electric field on cells and tissues. Since cells are
always surrounded by other cells, we studied how their interactions
influence the induced TMP. In the first part of our study, we studied
dependence of potential distribution on cell arrangement and density in
infinite cell suspensions where cells were organized into simple-cubic,
body-centered cubic, and face-centered cubic lattice. In the second part
of the study, we examined how induced TMP on a cell membrane is
dependent on its position inside a three-dimensional cell cluster.
Finally, the results for cells inside the cluster were compared to those
in infinite lattice. We used numerical analysis for the study,
specifically the finite-element method (FEM). The results for infinite
cell suspensions show that the induced TMP depends on both: cell volume
fraction and cell arrangement. We established from the results for
finite volume cell clusters and layers, that there is no radial
dependence of induced TMP for cells inside the cluster.
Laryngoscope. 2001 Jan;111(1):52-6.
Electroporation therapy for head and neck cancer including carotid artery involvement.
Allegretti JP, Panje WR.
Department of Otolaryngology, Rush-Presbyterian-St Luke’s Medical Center, Rush Medical College, Chicago, Illinois 60612, USA.
OBJECTIVES: Electroporation therapy with intralesional bleomycin
(EPT) is a novel, technically simple outpatient technique in which
high-voltage electric impulses delivered into a neoplasm transiently
increase cell membrane permeability to large molecules, including
cytotoxic agents, causing localized progressive necrosis. Unlike many
laser ablation methods, EPT can treat bulky tumors (>2 cm) with
complete penetration. Our recent publication confirms an excellent
response rate in the use of EPT in a clinical trial. STUDY
DESIGN, PATIENTS, AND METHODS: Following our initial prospective
study report in 1998, we have followed our entire initial cohort (10
patients) of patients with head and neck cancer beyond 24-months
follow-up. Additionally, we have used this approach to treat four
additional patients (total: 9 males/5 females) with upper aerodigestive
tract squamous cell carcinoma, including three with internal carotid
artery (ICA) involvement up to or within the skull base. Two patients
underwent preoperative balloon test occlusion with cerebral perfusion
studies followed by carotid embolization. EPT was then done safely at
least 2 weeks later to avoid the temporary hypercoagulable state.
RESULTS: Within the overall cohort (14 patients) 6 patients had a
complete response, 6 had a partial response, and 2 did not respond
(overall 85.7% response rate). Both patients with ICA involvement had a
partial or complete response to treatment; neither patient had a
hemorrhagic or neurologic complication. Overall, 13 of the 14 patients
were treated for persistent or recurrent head and neck cancer. Two of
the four patients with early recurrent stage tumors had no evidence of
recurrence after EPT with an average follow-up of 31.5 months. The
overall early stage tumor group had four complete responders out of five
(80%). On the contrary, only 2 of 9 patients with advanced recurrent
stage tumors were disease-free at 18 months. Morbidity was low for early
stage tumors, but higher for advanced tumors with complications,
including poor wound healing, dysphagia, and osteomyelitis. There were
no treatment-related deaths.
CONCLUSION: We found EPT to be safe and efficacious in patients with
head and neck cancer, even with internal carotid artery involvement.
Patients with early stage recurrences have the potential for prolonged
survival beyond 2 years without the morbidity of surgery and radiation
or toxicity of systemic chemotherapy. Because of its superb access
qualities even for bulky tumors, EPT is a potential method of delivery
for other tumoricidal agents such as in genetic-altering schemes.
J Membr Biol. 1984;78(1):53-60.
Electric field-induced breakdown of lipid bilayers and cell membranes: a thin viscoelastic film model.
A simple viscoelastic film model is presented, which predicts a
breakdown electric potential having a dependence on the electric pulse
length which approximates the available experimental data for the
electric breakdown of lipid bilayers and cell membranes (summarized in
the reviews of U. Zimmermann and J. Vienken, 1982, J. Membrane Biol.
67:165 and U. Zimmermann, 1982, Biochim. Biophys. Acta 694:227). The
basic result is a formula for the time tau of membrane breakdown (up to
the formation of pores): tau = alpha (mu/G)/(epsilon 2m epsilon 2oU4/24
sigma Gh3 + T2/sigma Gh-1), where alpha is a proportionality coefficient
approximately equal to ln(h/2 zeta o), h being the membrane thickness
and zeta o the amplitude of the initial membrane surface shape
fluctuation (alpha is usually of the order of unity), mu represents the
membrane shear viscosity, G the membranes shear elasticity modules,
epsilon m the membrane relative permittivity, epsilon o = 8.85 X 10(-12)
F/m, U the electric potential across the membrane, sigma the membrane
surface tension and T the membrane tension. This formula predicts a
critical potential Uc; Uc = (24 sigma Gh3/epsilon 2m epsilon 2o)1/4 (for
tau = infinity and T = 0). It is proposed that the time course of the
electric field-induced membrane breakdown can be divided into three
stages: (i) growth of the membrane surface fluctuations, (ii) molecular
rearrangements leading to membrane discontinuities, and (iii) expansion
of the pores, resulting in the mechanical breakdown of the membrane.
Biophys Chem. 1984 May;19(3):211-25.
Stochastic model for electric field-induced membrane pores. Electroporation.
Sugar IP, Neumann E.
Electric impulses (1-20 kV cm-1, 1-5 microseconds) cause transient
structural changes in biological membranes and lipid bilayers, leading
to apparently reversible pore formation ( electroporation ) with
cross-membrane material flow and, if two membranes are in contact, to
irreversible membrane fusion ( electrofusion ). The fundamental process
operative in electroporation and electrofusion is treated in terms of a
periodic lipid block model, a block being a nearest-neighbour pair of
lipid molecules in either of two states: (i) the polar head group in the
bilayer plane or (ii) facing the centre of a pore (or defect site). The
number of blocks in the pore wall is the stochastic variable of the
model describing pore size and stability. The Helmholtz free energy
function characterizing the transition probabilities of the various pore
states contains the surface energies of the pore wall and the planar
bilayer and, if an electric field is present, also a dielectric
polarization term (dominated by the polarization of the water layer
adjacent to the pore wall). Assuming a Poisson process the average
number of blocks in a pore wall is given by the solution of a non-linear
differential equation. At subcritical electric fields the average pore
size is stationary and very small. At supercritical field strengths the
pore radius increases and, reaching a critical pore size, the membrane
ruptures (dielectric breakdown). If, however, the electric field is
switched off, before the critical pore radius is reached, the pore
apparently completely reseals to the closed bilayer configuration
(reversible electroporation ).