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Portet Thomas

par Portet Thomas - 21 janvier 2010

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PhD student in the PhyStat group at Laboratoire de Physique Théorique, and in the Cellular Biophysics group at Institut de Pharmacologie et de Biologie Structurale.

Thesis title : Electropermeabilization of Model Systems

To download my thesis manuscript, click here.

To send me an e-mail, click here.

Pour consulter cette page en français, cliquez ici.

A short description of my research

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Biological membranes can be permeabilized in a very elegant and easy manner by subjecting cells to a sequence of electric pulses. With suitably chosen pulse duration and amplitude, this permeabilization is reversible and does not affect cell viability. This process, called electropermeabilization or electroporation, has led to various applications, for example in the fight against cancer or in the field of gene therapies. Despite its increasing popularity among scientists, we do not know precisely how an electropermeabilized membrane reorganizes at the microscopic level. An accurate description of electroporation would help to design new therapeutic protocols and to ensure their safety. The aim of my thesis is to try to improve our understanding of electropermeabilization, using both experimental and theoretical approaches.

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Most of my experimental work is conducted on lipid model systems. I use giant unilamellar vesicles (GUVs) to investigate the effect of electric fields on lipid bilayers of simple and well-defined composition. For example, we reported that size shrinkage of electroporated EggPC and DOPC GUVs could be used to measure the critical voltage inducing membrane permeabilization. Figure on the right shows the size decrease of an electroporated GUV, and lipid expulsion via the formation of tubular structures.

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Another part of my work consisted in the analysis of electromediated DNA uptake into GUVs. It is possible to monitor the amount of DNA in a liposome during an electropermeabilization protocol. The top row of the adjacent figure shows a giant vesicle (red channel) before (left picture) and after (right picture) electric treatment. One can see that no DNA (green channel) is initially present in the vesicle, and that field application causes DNA entry into the GUV. I also perform numerical studies of macromolecule entry in objects of various physical properties mimicking GUVs or real cells, by solving an electrodiffusion equation with the finite element calculus software Comsol. This aspect of my work is illustrated by the bottom row of the figure on the right, showing the concentration increase of a marker molecule in a spherical object.

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Using fast digital imaging, one can visualize the closure of electric field-induced macropores in giant vesicles, as shown on the figure on the right. During my research internship in the group of R. Dimova, I have developed a new method for measuring edge tensions in lipid bilayers, which is based on the analysis of the pore closure rate. If this stage of pore closure is pretty well described by current theories, the mechanisms of pore opening still remain to be elucidated. I am performing work in this direction, by exploring micrsocopic models of electroporation via the use of Monte Carlo simulations.