Effects of sodium chloride concentration on the electroporation induced rate constant of rupture of vesicles

Abstract

Vesicles with nano-to micrometer in diameter are basically a closed and spherical structure formed by a double layer of lipids. Irreversible electroporation (IRE) induced lateral electric tension in the membranes of giant unilamellar vesicles (GUVs) of sizes like biological cells. In this study, the effects of sodium chloride concentration in the buffer on the IRE-induced probability of pore formation and the rate constant (kp) of rupture of GUVs have been investigated. The GUVs were prepared using a mixture of negatively charged lipid dioleoylphosphatidylglycerol (DOPG) and neutral lipid dioleoylphosphatidylcholine (DOPC) using the well known natural swelling method at salt concentration 62, 162 and 262 mM in the buffer. The IRE signal of pulsating direct current was applied to the GUVs through a gold coated electrode system. The probability of pore formation increased with the increase of electric tension. The time course of the fraction of intact GUVs among all the examined GUVs was fitted with a single exponential decay function and calculated the values of kp. The values of kp were obtained (1.8 ± 0.1)×10-2, (5.4 ± 0.4)×10-2 and (16.0 ± 0.4)×10-2 s-1 at electric tension 4.5, 5.5 and 6.5 mN/m for 62 mM salt, respectively. The similar tendency of increasing the values of kp with electric tension was also obtained for 162 and 262 mM salt. The decrease of salt concentration showed higher kp and higher probability of pore formation at a particular tension. The rate constant of rupture was fitted to the theoretical equation and the line tension of membranes was obtained, which increased with the decrease of salt concentration. The decrease in the energy barrier of a prepore state with the decrease of salt concentration is the main factor to increase the kp.