Membrane curvature and high-field electroporation of lipid bilayer vesicles

The turbidity relaxations of small unilamellar lipid vesicles, vesicle radii a/nm = 25, 38, 80, and 170, prepared from commercial 20% (weight) lecithin in 0.2 mM NaCl aqueous solution exposed to a rectangular field pulse of field strengths in the range 0 < E/MV m(-1) less than or equal to 8 indicate vesicle electro-elongation coupled to smoothing of membrane thermal undulations and membrane stretching as well as membrane electroporation (MEP). If compared at the same nominal transmembrane potential, here Deltaphi(N) = - 1.5Ea = -0.3 V, at the pole caps and at zero membrane conductivity, the decrease in the vesicle radius leads to an increase in the fraction f(p), = DeltaS(p)/S-0 of porated membrane area from f(p) = 1.0 x 10(-3) at a = 170 nm to f(p)= 2.9 x 10(-2) at a = 25 nm. The effect of the membrane curvature on MEP is specified in terms of the difference in the lipid packing density in the outer and inner membrane leaflets. The formation of one mole of pores of mean radius (r) over bar (p) = 0.35 +/- 0.05 nm is accompanied with the dissipation of the molar area difference elasticity energy of Delta(r)G(ADE) -3.2RT at the vesicle radius a = 25 nm and of DeltarG(ADE) = -0.5RT at a = 170 nm, where R is the gas constant and T = 293 K (20 degreesC). In brief, membrane curvature favors electric pore formation.