Visualization of membrane loss during the shrinkage of giant vesicles under electropulsation

📝 Abstract

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.

💡 Analysis

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.

📄 Content

Visualization of membrane loss during the shrinkage of giant vesicles under electropulsation Thomas Portet Institut de Pharmacologie et de Biologie Structurale, CNRS UMR 5089, Universit´e Paul Sabatier, Toulouse, France and Laboratoire de Physique Th´eorique, CNRS UMR 5152, Universit´e Paul Sabatier, Toulouse, France. Franc Camps i Febrer Institut de Pharmacologie et de Biologie Structurale, CNRS UMR 5089, Universit´e Paul Sabatier, Toulouse, France. Jean-Michel Escoffre Institut de Pharmacologie et de Biologie Structurale, CNRS UMR 5089, Universit´e Paul Sabatier, Toulouse, France. Cyril Favard Institut Fresnel, CNRS UMR 6133, Marseille, France. Marie-Pierre Rols Institut de Pharmacologie et de Biologie Structurale, CNRS UMR 5089, Universit´e Paul Sabatier, Toulouse, France. David S. Dean 1 Laboratoire de Physique Th´eorique, CNRS UMR 5152, Universit´e Paul Sabatier, Toulouse, France. August 4, 2021 arXiv:0805.3600v2 [cond-mat.soft] 15 Jan 2010 Membrane Loss in Electroporated GUVs 2 1Corresponding author. Address: Laboratoire de Physique Th´eorique, CNRS UMR 5152, Universit´e Paul Sabatier, 118 Route de Narbonne, Toulouse, 31062, France. Tel.: (0033)561556463, Fax: (0033)561556065 Abstract 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 modes of membrane loss were directly observed: pore formation, vesicle formation and tubule formation. Key words: giant liposomes; electroporation; vesicles; pores; tubules Membrane Loss in Electroporated GUVs 2 ABBREVIATIONS - LIST OF SYMBOLS EggPC: L-α-Phosphatidylcholine (Egg, Chicken) DOPC: 1,2-Dioleoyl-sn-Glycero-3-Phosphocholine DiIC18: 1,1’-dioctadecyl-3,3,3’,3’-tetramethylindocarbocyanine perchlorate Rhodamine PE: L-α-Phosphatidylethanolamine-N-(Egg Lissamine Rhodamine PE) E: magnitude of the applied electric field ∆Ψ: transmembrane voltage ∆Ψ0: initial transmembrane voltage induced by the first pulse at the poles of the liposomes. ∆Ψc: critical transmembrane voltage n: number of pulses R(n): radius of the vesicle after n pulses Rc: critical radius W(n): rescaled radius of the vesicle after n pulses R(n)/R(0) Wc: rescaled critical radius Rc/R(0) λ: fraction of the permeabilized area lost per pulse Nc: number of pulses needed to enter the shrinking regime q: probability that one pulse induces a transition from the pre-shrinking to the shrinking regime SR: shrinking regime PR: pre-shrinking regime a: membrane thickness ae: membrane electrical thickness ϵm: membrane dielectric constant C: constant depending on R, a and the various conductivities of the problem θ: angle on the cell surface with respect to the direction of the applied field Membrane Loss in Electroporated GUVs 3 θc: critical angle A: area of the vesicle Ap: permeabilized area Σ0: initial surface tension Σel: surface tension induced by the electric field Σlys: lysis tension p: dipole moment of the PC headgroup l: length of the hydrocarbon chain ρ: effective radius of the lipid hydrocarbon tail viewed as a cylinder µ: lipid tail hydrophobic free energy per unit of area INTRODUCTION Electropermeabilization is a commonly used physical method where electric pulses are applied to cells and vesicles and has been widely reviewed in the literature (1–7). An effect, of major impor- tance, of the electric pulses is that under certain circumstances they can induce the transient per- meabilization of the cell plasma membrane. This permeabilization manifests itself via the crossing of the cell membrane by molecules which would normally not be able to permeate the cell mem- brane. When subjected to sufficiently large electric fields, vesicle membranes become permeable to small molecules (8, 9) and flat membranes show a marked increase in their electrical conductance (10). Small molecules appear to cross permeabilized membranes via simple diffusion. However complex processes, such as electrophoresis and direct interactions with the membrane, come into play for larger molecules such as DNA. Electropermeabilization is now regularly employed as a delivery method for a large variety of molecules such as drugs, antibodies, oligonucleotides, RNA and DNA (6, 9, 11–13). Initial studies were carried out in vitro on cells in culture, but as the technique has developed an increasing amount of data has been obtained in vivo on tissues (14–16) and the method is being adapted to the clinical context (17, 18). Clearly the method has a huge potential in the fields of cancer treatment and gene therapy, offering, in some cases more efficient, more controllable and safer treatment p

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