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This paper describes the biological response of cultured HeLa S3 cells to non-thermal, intense burst sinusoidal electric fields (IBSEF). The proliferation activity of the cells subjected to 300 kV/m, 200 μs-long IBSEF with a frequency between 0.3 MHz and 100 MHz was evaluated by using an automatic cell event monitor, xCELLigence, for 48 hours. The experiment showed that the cell proliferation depended on the pulse number and the frequency band of the IBSEF. The application of the smaller number of the pulses enhances the proliferation, whereas the large number of pulses tends to kill the cells. The dependence on the pulse number indicates the effect of the pulse is accumulated. The cells seem to be more sensitive to the pulses at the lower frequencies less than 1 MHz. The frequency of 100 MHz, which is sufficiently large for the field to penetrate into the cell, did not appear to influence the proliferation and the immediate death process. When the cells were subjected to 30 pulses of 3 MHz IBSEF, the proliferation was promoted 1.6 times as fast as that of the sham exposure. The frequency dependence of the proliferation might be associated with the electrical stress at the plasma membrane where several proteins related to the cell cycling are located. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]