155 research outputs found
Visualization of membrane loss during the shrinkage of giant vesicles under electropulsation
We study the effect of permeabilizing electric fields applied to two
different types of giant unilamellar vesicles, the first formed from EggPC
lipids and the second formed from DOPC lipids. Experiments on vesicles of both
lipid types show a decrease in vesicle radius which is interpreted as being due
to lipid loss during the permeabilization process. We show that the decrease in
size can be qualitatively explained as a loss of lipid area which is
proportional to the area of the vesicle which is permeabilized. Three possible
mechanisms responsible for lipid loss were directly observed: pore formation,
vesicle formation and tubule formation.Comment: Final published versio
Tension-voltage relationship in membrane fusion and its implication in exocytosis
AbstractIn this study, new methods are used to control cellular membrane tension to evaluate the role it plays in electrofusion. The data show that membrane tension present during the application of an electric field facilitates electro-induced membrane fusion. No enhancement was detected if the strain was applied after the pulse. Analysis of the electromechanical process of fusion revealed a synergy between the two kinds of constraints in the membrane fusion. Both mechanical and electrical constraints apparently play a key role in membrane fusion between the granule membrane and the plasma membrane, i.e. the exocytosis process
A lattice model for the kinetics of rupture of fluid bilayer membranes
We have constructed a model for the kinetics of rupture of membranes under
tension, applying physical principles relevant to lipid bilayers held together
by hydrophobic interactions. The membrane is characterized by the bulk
compressibility (for expansion), the thickness of the hydrophobic part of the
bilayer, the hydrophobicity and a parameter characterizing the tail rigidity of
the lipids. The model is a lattice model which incorporates strain relaxation,
and considers the nucleation of pores at constant area, constant temperature,
and constant particle number. The particle number is conserved by allowing
multiple occupancy of the sites. An equilibrium ``phase diagram'' is
constructed as a function of temperature and strain with the total pore surface
and distribution as the order parameters. A first order rupture line is found
with increasing tension, and a continuous increase in proto-pore concentration
with rising temperature till instability. The model explains current results on
saturated and unsaturated PC lipid bilayers and thicker artificial bilayers
made of diblock copolymers. Pore size distributions are presented for various
values of area expansion and temperature, and the fractal dimension of the pore
edge is evaluated.Comment: 15 pages, 8 figure
Phase state dependent current fluctuations in pure lipid membranes
Current fluctuations in pure lipid membranes have been shown to occur under
the influence of transmembrane electric fields (electroporation) as well as a
result from structural rearrangements of the lipid bilayer during phase
transition (soft perforation). We demonstrate that the ion permeability during
lipid phase transition exhibits the same qualitative temperature dependence as
the macroscopic heat capacity of a D15PC/DOPC vesicle suspension. Microscopic
current fluctuations show distinct characteristics for each individual phase
state. While current fluctuations in the fluid phase show spike-like behaviour
of short time scales (~ 2ms) with a narrow amplitude distribution, the current
fluctuations during lipid phase transition appear in distinct steps with time
scales in the order of ~ 20ms. 1 We propose a theoretical explanation for the
origin of time scales and permeability based on a linear relationship between
lipid membrane susceptibilities and relaxation times in the vicinity of the
phase transition.Comment: 22 pages including 6 figure
A Theoretical Analysis of the Feasibility of a Singularity-Induced Micro-Electroporation System
Electroporation, the permeabilization of the cell membrane lipid bilayer due to a pulsed electric field, has important implications in the biotechnology, medicine, and food industries. Traditional macro and micro-electroporation devices have facing electrodes, and require significant potential differences to induce electroporation. The goal of this theoretical study is to investigate the feasibility of singularity-induced micro-electroporation; an electroporation configuration aimed at minimizing the potential differences required to induce electroporation by separating adjacent electrodes with a nanometer-scale insulator. In particular, this study aims to understand the effect of (1) insulator thickness and (2) electrode kinetics on electric field distributions in the singularity-induced micro-electroporation configuration. A non-dimensional primary current distribution model of the micro-electroporation channel shows that while increasing insulator thickness results in smaller electric field magnitudes, electroporation can still be performed with insulators thick enough to be made with microfabrication techniques. Furthermore, a secondary current distribution model of the singularity-induced micro-electroporation configuration with inert platinum electrodes and water electrolyte indicates that electrode kinetics do not inhibit charge transfer to the extent that prohibitively large potential differences are required to perform electroporation. These results indicate that singularity-induced micro-electroporation could be used to develop an electroporation system that consumes minimal power, making it suitable for remote applications such as the sterilization of water and other liquids
Diffusion-Weighted MRI for Verification of Electroporation-Based Treatments
Clinical electroporation (EP) is a rapidly advancing treatment modality that uses electric pulses to introduce drugs or genes into, e.g., cancer cells. The indication of successful EP is an instant plasma membrane permeabilization in the treated tissue. A noninvasive means of monitoring such a tissue reaction represents a great clinical benefit since, in case of target miss, retreatment can be performed immediately. We propose diffusion-weighted magnetic resonance imaging (DW-MRI) as a method to monitor EP tissue, using the concept of the apparent diffusion coefficient (ADC). We hypothesize that the plasma membrane permeabilization induced by EP changes the ADC, suggesting that DW-MRI constitutes a noninvasive and quick means of EP verification. In this study we performed in vivo EP in rat brains, followed by DW-MRI using a clinical MRI scanner. We found a pulse amplitude–dependent increase in the ADC following EP, indicating that (1) DW-MRI is sensitive to the EP-induced changes and (2) the observed changes in ADC are indeed due to the applied electric field
Apoptosis- and necrosis-induced changes in light attenuation measured by optical coherence tomography
Optical coherence tomography (OCT) was used to determine optical properties of pelleted human fibroblasts in which necrosis or apoptosis had been induced. We analysed the OCT data, including both the scattering properties of the medium and the axial point spread function of the OCT system. The optical attenuation coefficient in necrotic cells decreased from 2.2 ± 0.3 mm−1 to 1.3 ± 0.6 mm−1, whereas, in the apoptotic cells, an increase to 6.4 ± 1.7 mm−1 was observed. The results from cultured cells, as presented in this study, indicate the ability of OCT to detect and differentiate between viable, apoptotic, and necrotic cells, based on their attenuation coefficient. This functional supplement to high-resolution OCT imaging can be of great clinical benefit, enabling on-line monitoring of tissues, e.g. for feedback in cancer treatment
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