Chapter 2 Electric Conductance of Planar Lipid Bilayer as a Tool for the Study of Membrane Pore Selectivity and Blockade

Abstract Despite the very low thickness, the lipid bilayer of biomembrane presents an efficient permeability barrier to polar substances such as water or ions. Biophysical approach to membrane permeability study includes among others the pure lipid pores appeared at the membrane lipid phase transition [Antonov et al. in: A. Leitmannova Liu, H.T. Tien (Eds.) Advances in Planar Lipid Bilayers and Liposomes, Academic Press, Amsterdam, 2005 pp. 151–173)] [ 1 ]. This approach belongs to the methods of soft poration of planar BLM (pBLM) based on the structural rearrangement of the lipid bilayer at the phase transition of membrane lipid from liquid crystalline state to the gel one. This allows us to avoid the unexpected influence of high electrical field at electroporation on chemical components of the BLM. This chapter is aimed an experimental and theoretical study of soft poration method and its application to the problem of lipid pore ion selectivity and conductance blockade. It was shown recently [V.F. Antonov, A.A. Anosov, V.P. Norik, E.Yu. Smirnova, Eur. Biophys. J. 34 (2005) 155–162)] [ 2 ] that the dependence of electric conductance in single lipid pore on the poly(ethylene)glycols (PEGs) size in water solution resembled the behavior of reconstructed protein pores like alamethicin channel [S.M. Bezrukov, I. Vodyanoy, Biophys. J. 64 (1993) 16–25] [ 3 ]. When a PEG with a low molecular weight was added to the medium, the pore conductance dropped by the same factor as the bulk conductivity. Increasing of the PEG molecular weight was followed by a nearly complete blockade of single lipid pore conductance in 1 M LiCl. However, as the size of the PEG added was increased more, there was a recovery in conductance as the PEG was progressively excluded from the pore interior. It is shown that PEG‐1450 being added to bulk solution strongly influences the cation selectivity of BLM: while PEG‐1450 completely blocks ion conductance in 1 M LiCl, it does not block ion conductance in 1 M CsCl. Experimentally observed in our study, complete blockade of lipid pores in the presence of PEGs, and change of ion selectivity could be attributed to prevent the conversion of hydrophobic lipid pore into hydrophilic one in evolution of lipid pore occurred at lipid phase transition.