Electric pulses are known to affect the outer membrane and intracellular structures of tumour cells. By applying electrical pulses of 450 ns duration with electric field intensity of 8 kV/cm to HepG2 cells for 30 s, electric pulse-induced changes in the integrity of the plasma membrane, apoptosis, viability and mitochondrial transmembrane potential were investigated. Results demonstrated that electric pulses induced cell apoptosis and necrosis accompanied with the decrease of mitochondrial transmembrane potential and the formation of pores in the membrane. The role of cytoskeleton in cellular response to electric pulses was investigated. We found that the apoptotic and necrosis percentages of cells in response to electric pulses decreased after cytoskeletal disruption. The electroporation of cell was not affected by cytoskeletal disruption. The results suggest that the disruption of actin skeleton is positive in protecting cells from killing by electric pulses, and the skeleton is not involved in the electroporation directly.

The application of nanosecond pulsed electric fields (nsPEFs) is a novel method to induce the death of cancer cells. NsPEFs could directly function on the cell membrane and activate the apoptosis pathways, then induce apoptosis in various cell lines. However, the nsPEFs-inducing-apoptosis action sites and the exact pathways are not clear now. In this study, nsPEFs were applied to the human liver cancer cells HepG2 with different parameters. By apoptosis assay, morphological observation, detecting the mitochondrial membrane potential (ΔΨ ), intracellular calcium ion concentration ([Ca]i) and the expressions of key apoptosis factors, we demonstrated that nsPEFs could induce the morphology of cell apoptosis, the change in ΔΨ , [Ca]i and the upregulation of some key apoptosis factors, which revealed the responses of liver cancer cells and indicated that cells may undergo apoptosis through the mitochondria-dependent pathway after nsPEFs were applied.

The goal of this study was to assess the effect of nanosecond electric pulses on HepG2 human liver cancer cells. Electric pulses with a high strength of 10 kV/cm, duration of 500 ns and frequency of 1 Hz were applied to the cells. After delivery of electric pulses, apoptosis, intracellular calcium ion concentrations, transmembrane mitochondrial potentials, electropermeabilization and recovery from electropermeabilization in cells were investigated. The results showed that electric pulse treatment for 20 s and more could trigger apoptosis in cells. Real-time observation indicated an immediate increase in intracellular calcium ion concentration and a dramatic decrease in mitochondrial membrane potential in cells responding to electric pulses. In subsequent experiments, propidium iodide uptake in cells emerged after exposure to electric pulses, indicating electropermeabilization of the cell membrane. Furthermore, recovery from electropermeabilization was not observed even 4 h after the stimulation, demonstrating that irreversible electropermeabilization was induced by electric pulses. In conclusion, electric pulses with a high strength and nanosecond duration can damage cancer cells, accompanied by a series of intracellular changes, providing strong evidence for the application of electric pulses in cancer treatment.

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