Permeability modes in fluctuating lipid membranes with DNA-translocating pores.

Membrane pores can significantly alter not only the permeation dynamics of biological membranes but also their elasticity. Large membrane pores able to transport macromolecular contents represent an interesting model to test theoretical predictions that assign active-like (non-equilibrium) behavior to the permeability contributions to the enhanced membrane fluctuations existing in permeable membranes [Maneville et al. Phys. Rev. Lett. 82, 4356 (1999)]. Such high-amplitude active contributions arise from the forced transport of solvent and solutes through the open pores, which becomes even dominant at large permeability. In this paper, we present a detailed experimental analysis of the active shape fluctuations that appear in highly permeable lipid vesicles with large macromolecular pores inserted in the lipid membrane, which are a consequence of transport permeability events occurred in an osmotic gradient. The experimental results are found in quantitative agreement with theory, showing a remarkable dependence with the density of membrane pores and giving account of mechanical compliances and permeability rates that are compatible with the large size of the membrane pore considered. The presence of individual permeation events has been detected in the fluctuation time-series, from which a stochastic distribution of the permeation events compatible with a shot-noise has been deduced. The non-equilibrium character of the membrane fluctuations in a permeation field, even if the membrane pores are mere passive transporters, is clearly demonstrated. Finally, a bio-nano-technology outlook of the proposed synthetic concept is given on the context of prospective uses as active membrane DNA-pores exploitable in gen-delivery applications based on lipid vesicles.

Bimodal spectrum for the curvature fluctuations of bilayer vesicles: pure bending plus hybrid curvature-dilation modes.

We study thermal undulations of giant bilayer vesicles by flickering spectroscopy. The experimental fluctuation spectra are scrutinized in view of the classical Helfrich theory. Pure bending modes are revealed to be unable to predict the large fluctuations systematically found at a high wave vector. Hybrid curvature-dilational modes are then invoked as a more efficient mode of motion in producing high curvatures. A bimodal spectrum of the thermal undulations has been theoretically developed for the shell-like topology. Reconciliation between experiments and theory is achieved when this bimodal spectrum is considered.