Conductometric and electrooptic relaxation spectrometry of lipid vesicle electroporation at high fields

Abstract

Electrooptic and conductometric relaxation spectrometry of lipid unilamellar vesicles (Avanti 20) of radius a = 90 nm, filled with 0.2 M NaCl electrolyte, suspended in low conductive 0.33 M sucrose and 0.2 mM NaCl solution of vesicle number density ρ_v ≈ 2.4 × 10¹⁵ L⁻¹ and exposed to a rectangular electric field pulse (up to E = 7.5 MV m⁻¹, pulse duration t_E = 10 µs) has been used to quantify the structural changes involved in membrane electroporation (ME) and rapid membrane transport, sometimes also called electropermeation (MP), as well as extent and rate of shape deformations. The data are consistent with the formation of ion-conductive membrane pores contributing to conductance not only via the ionic vesicle interior but also by releasing intravesicular electrolyte through the pores during the electric pulse, dominantly by interactive electrodiffusion. The surface area fraction f_p and the conductivity λ_p of the membrane pores increase with increasing field strength, 0 ≤ E/MV m⁻¹ ≤ 7.5, in the ranges 0 ≤ f_p ≤ 1.4 × 10⁻² and 0 ≤ λ_p/S m⁻¹ ≤ 2.7 × 10⁻³, respectively. The data analysis suggests that electrostatic interactions between the ions and the low dielectric pore wall are the origin of the very small values of the Nernst distribution coefficient, e.g. = 6.6 × 10⁻⁴ at E = 7.5 MVm⁻¹. The pore conductivity λ_p and are non-linear functions of the applied electric field, yielding a field-independent pore transport length l_p = 0.56 nm. In summary, the new analytical proposal establishes quantitative relationships between structural electroporation quantities and characteristic parameters of the small ion transport or electropermeation.