Biotech, Biomaterials and Biomedical: TechConnect Briefs 2016Biotech, Biomaterials and Biomedical TechConnect Briefs 2016

Cancer Nanotechnology Chapter 5

Estimation of the Energetic Barrier to Pore Formation and the Pore Radius Corresponding to this Barrier for Different Cell Lines

A. Bitinaitė, R. Saulė, G. Saulis
Vytautas Magnus University, Lithuania

pp. 152 - 155

Keywords: electroporation, potassium ions, rat glioma, mouse hepatoma, CHO, human erythrocytes

The permeability of the cell membrane can be modified by exposing of cells to high-voltage electric pulses leading to the formation of nanometer-sized pores in the cell membrane (electroporation or nanoporation). This phenomenon is widely used in cell biology, biotechnology and medicine. Earlier, optimal electrical parameters for electroporation of cells used to be determined empirically for each particular cell line. Now before real experiments, it is already possible to get theoretical relationships between various parameters the electric field treatment (field strength, duration, number of pulses, etc.) required to electroporate the cell. Just such parameters as the energy barrier to pore formation at zero transmembrane potential Wf(0) and the pore radius r* corresponding to to the top of this barrier have to be known. Unfortunately, these parameters have been estimated just for a few cell lines, which makes difficult obtaining theoretical predictions for other types of cells because the range of the variations of the values of these parameters between different cell lines is not known yet. Thus, it is still difficult to predict individual responses of different cells to electric treatment. The aim of this study was to estimate the energy barrier to pore formation at zero transmembrane potential Wf(0) and the pore radius r* corresponding to the top of this barrier for four different cell lines, both cancerous and non-cancerous ones. The energy barrier to pore formation Wf(0) and the pore radius r* were estimated by comparing a theoretical dependence of the electric field strength required to create a single pore in the cell with the experimental dependences of the field strength at which 50% of cells become electroporated on the pulse duration. Experiments were performed with two non-tumor cell lines (human erythrocytes and Chinese hamster ovary (CHO) cells) and two tumor cell lines (mouse hepatoma MH-22A and rat glioma C6 cells). The cells were exposed to a single square-wave pulse with the duration of 95 ns–2 ms and the electric field strength was varied from 0.6 to 15 kV/cm for erythrocytes and from 0.2 to 7.5 kV/cm for CHO, MH-22A, and C6 cells. The fraction of electroporated cells was determined from the extent of the release of intracellular potassium ions. The dependencies of the fraction of electroporated cells on the electric field strength were obtained for different pulse durations. From these relationships the pulse amplitude inducing electroporation of 50% of cells was estimated for each pulse length. By comparing theoretical dependencies of the electric field strength required to create a single pore in the cell with the experimental data, the energy barrier Wf(0) and the pore radius r* were estimated for each cell line. The parameters were found using the least-squares method. The best fit for was obtained for Wf(0) = 41–42 kT, and r* = 0.3–0.35 nm. This study was in part supported by grant 31V-36 from the Lithuanian Agency for Science, Innovation and Technology (to GS).