Effect of pulsing sequence of nanosecond pulsed electric fields on viability of HeLa S3 cells

This study elucidates the influence of the pulsing sequence of repetitive nanosecond pulsed electric fields on the viability of human cancer (HeLa S3) cells. A magnetic pulse compressor was used to repetitively deliver 70 ns-long high voltage pulses to cultured HeLa cells in a 4 mm-gap cuvette electrode. The repetition frequency was varied between 0.01 and 250 pulses per second (pps), corresponding to interval from 100 to 0.004 s, respectively. The electric field and the number of pulses were fixed at 25 kV/cm and 25, respectively, which is a sub-lethal condition for the cells. Propidium iodide was used to identify dead cells in the population. Statistical analysis of a cell death ratio in approximately 5000 cells was performed using a flow cytometer. This experiment shows repetition frequency affects cell viability even with identical intra-medium electrical energy expenditure. The dead cell ratio was increased with decreasing pulse repetition frequency down to 0.33 pps, whereas the ratio is decreased with decreasing frequency below 0.1 pps. Since the resealing mechanism of nano-pores caused by the application of ns pulse lasts for a minute, the dependence of the cell viability on the pulsing sequence might be associated with time constants of biological processes related to recovery from field-induced damage.