Activation energy for pore opening in lipid membranes under an electric field

International audienceThe standard model of pore formation was introduced more than fifty years ago, and it has been since, despite some refinements, the cornerstone for interpreting experiments related to pores in membranes. A central prediction of the model concerning pore opening under an electric field is that the activation barrier for pore formation is lowered proportionally to the square of the electric potential. However, this has only been scarcely and inconclusively confronted to experiments. In this paper, we study the electropermeability of model lipid membranes composed of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) containing different fractions of POPC-OOH, the hydroperoxidized form of POPC, in the range 0 to 100 mol %. By measuring ion currents across a 50-μm-diameter black lipid membrane (BLM) with picoampere and millisecond resolution, we detect hydroperoxidation-induced changes to the intrinsic bilayer electropermeability and to the probability of opening angstrom-size or larger pores. Our results over the full range of lipid compositions show that the energy barrier to pore formation is lowered linearly by the absolute value of the electric field, in contradiction with the predictions of the standard model

Cargo self-assembly rescues affinity of cell-penetrating peptides to lipid membranes

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Nature of the Polyanion Governs the Antimicrobial Properties of Poly(arginine)/Polyanion Multilayer Films

International audienceCoatings with antimicrobial properties are garnering interest to prevent implant-associated infections. Recently, we showed that poly(arginine)/hyaluronic acid (PAR/HA) multilayers built with PAR chains constituted from 30 arginine residues (PAR30) have strong antimicrobial properties through a contact-killing mechanism. This property is due to the ability of PAR30 chains, when associated with HA, to diffuse in the multilayer. Here, we investigate the effect of the nature of the polyanion on the antimicrobial activity of (PAR30/polyanion) multilayers. Four polysaccharides, one polypeptide, and one synthetic polyelectrolyte are investigated. Surprisingly, only HA leads to films with antimicrobial character. We relate this property to the strong diffusion capacity of PAR30 chains in (PAR30/HA) multilayers compared to their diffusion ability in the other (PAR30/polyanion) films. Through isothermal microcalorimetry experiments, we also demonstrate that interactions in solutions of PAR30 chains with the different polyanions are characterized by a negative reaction enthalpy for all of the investigated polyanions except for HA, where the enthalpy of reaction is positive. Moreover, the molecular weight of HA is not a key parameter for the diffusion ability of PAR chains or for the bioactivity of the film. These results constitute an important step toward the establishment of rules to design contact-killing antimicrobial polyelectrolyte multilayer

Directly imaging emergence of phase separation in peroxidized lipid membranes

Lipid peroxidation plays an important role in cell signaling and disease as well as therapy, however, the effect on the membrane structure and mechanical behavior remains poorly understood. Here, the authors report the direct and quantitative measurement of the bilayer’s structure and viscoelastic properties upon peroxidation of lipid membranes