Size-controlled nanopores in lipid membranes with stabilizing electric fields.
ABSTRACT Molecular dynamics (MD) has been shown to be a useful tool for unveiling many aspects of pore formation in lipid membranes under the influence of an applied electric field. However, the study of the structure and transport properties of electropores by means of MD has been hampered by difficulties in the maintenance of a stable electropore in the typically small simulated membrane patches. We describe a new simulation scheme in which an initially larger porating field is systematically reduced after pore formation to lower stabilizing values to produce stable, size-controlled electropores, which can then be characterized at the molecular level. A new method allows the three-dimensional modeling of the irregular shape of the pores obtained as well as the quantification of its volume. The size of the pore is a function of the value of the stabilizing field. At lower fields the pore disappears and the membrane recovers its normal shape, although in some cases long-lived, fragmented pores containing unusual lipid orientations in the bilayer are observed.
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ABSTRACT: Formation of a water bridge across the lipid bilayer is the first stage of pore formation in molecular dynamic (MD) simulations of electroporation, suggesting that the intrusion of individual water molecules into the membrane interior is the initiation event in a sequence that leads to the formation of a conductive membrane pore. To delineate more clearly the role of water in membrane permeabilization, we conducted extensive MD simulations of water bridge formation, stabilization, and collapse in palmitoyloleoylphosphatidylcholine bilayers and in water-vacuum-water systems, in which two groups of water molecules are separated by a 2.8 nm vacuum gap, a simple analog of a phospholipid bilayer. Certain features, such as the exponential decrease in water bridge initiation time with increased external electric field, are similar in both systems. Other features, such as the relationship between water bridge lifetime and the diameter of the water bridge, are quite different between the two systems. Data such as these contribute to a better and more quantitative understanding of the relative roles of water and lipid in membrane electropore creation and annihilation, facilitating a mechanism-driven development of electroporation protocols. These methods can be extended to more complex, heterogeneous systems that include membrane proteins and intracellular and extracellular membrane attachments, leading to more accurate models of living cells in electric fields.Journal of Membrane Biology 05/2013; · 2.48 Impact Factor
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ABSTRACT: Electroporation is the basis for the transfection of genetic material and for drug delivery to cells, including electrochemotherapy for cancer. By means of Molecular Dynamics many aspects of membrane electroporation have been unveiled at the molecular detail in simple, homogeneous, lipid bilayers. However, the correspondence of these findings with the process happening in cell membranes require, at least, the consideration of laterally structured membranes. Here, I present a systematic Molecular Dynamics study of bilayers composed of different liquid-ordered and liquid-disordered lipid phases subjected to a transversal electric field. The simulations reveal two significant results. First, the electric field mainly affects the properties of the disordered phases, so that electroporation takes place in these membrane regions. Second, the smaller the disordered domains are, the faster they become electroporated. These findings may have a relevant significance in the experimental application of cell eletroporation in vivo since it implies that electro-induced and pore-mediated transport processes occur in particularly small disordered domains of the plasma membrane, thus locally affecting only specific regions of the cell.Biochimica et Biophysica Acta 10/2013; · 4.66 Impact Factor