Kinetics, Statistics, and Energetics of Lipid Membrane Electroporation Studied by Molecular Dynamics Simulations

Abstract

Membrane electroporation is the method to directly transfer bioactive substances such as drugs and genes into living cells, as well as preceding electrofusion. Although much information on the microscopic mechanism has been obtained both from experiment and simulation, the existence and nature of possible intermediates is still unclear. To elucidate intermediates of electropore formation by direct comparison with measured prepore formation kinetics, we have carried out 49 atomistic electroporation simulations on a palmitoyl-oleoyl-phosphatidylcholine bilayer for electric field strengths between 0.04 and 0.7 V/nm. A statistical theory is developed to facilitate direct comparison of experimental (macroscopic) prepore formation kinetics with the (single event) preporation times derived from the simulations, which also allows us to extract an effective number of lipids involved in each pore formation event. A linear dependency of the activation energy for prepore formation on the applied field is seen, with quantitative agreement between experiment and simulation. The distribution of preporation times suggests a four-state pore formation model. The model involves a first intermediate characterized by a differential tilt of the polar lipid headgroups on both leaflets, and a second intermediate (prepore), where a polar chain across the bilayer is formed by 3-4 lipid headgroups and several water molecules, thereby providing a microscopic explanation for the polarizable volume derived previously from the measured kinetics. An average pore radius of 0.47 +/- 0.15 nm is seen, in favorable agreement with conductance measurements and electrooptical experiments of lipid vesicles.

Electroporation of Asymmetric Phospholipid Membranes

“…13−15 In contrast, when an electric field is applied directly to the membrane, the pore continues to expand until the bilayer is ruptured due to the artifacts related to a combined use of periodic boundary conditions and the PME method. 12 To overcome this, one needs to considerably decrease an external electric field once the pore is formed. 12,23 Most computational studies by far have focused mainly on electroporation of single-component phospholipid bilayers which are usually considered as model systems for mimicking the structural properties of plasma membranes.…”

“…12 To overcome this, one needs to considerably decrease an external electric field once the pore is formed. 12,23 Most computational studies by far have focused mainly on electroporation of single-component phospholipid bilayers which are usually considered as model systems for mimicking the structural properties of plasma membranes. There are a few exceptions, though: Several groups reported electroporation phenomena in mixed bilayers.…”

<em>In Vivo</em> Microinjection and Electroporation of Mouse Testis

“…In general, EP is referred to as a dynamic phenomenon that depends on local transmembrane voltage with consequently mediated pores within nanoseconds. These gaps can be maintained for milliseconds, sufficient to grant access to DNA, RNA or small molecules 5 . When the applied voltage is too high, the usually transient character of EP is counteracted due to heat production and induction of too comprehensive permeabilization with consequent irreversible damage of the cell 5 .…”

Irreversible electroporation: the evolution of a laboratory technique to be used in interventional oncology

“…Currently, the transient aqueous pore hypothesis is the favored explanation for the physiologic effects of electroporation, and recent molecular dynamic simulations support this theory (5). By this hypothesis, electroporation entails the creation of nanoscale pores or defects in the cell membrane.…”