Modification of dielectric characteristics of cells by intense pulsed electric fields

The immediate charging response of a biological cell to pulsed electric field exposure depends strongly on the dielectric properties of its cellular components. Conversely, pulsed electric fields above a certain threshold of amplitude and duration will change these properties. Hence, an understanding of dielectric membrane phenomena is necessary to explain the underlying interaction mechanisms between a pulsed electric field and cells. Furthermore, different electrical characteristics of cells might also allow devising exposure conditions for pulsed electric field treatments that can preferentially target specific cells, such as cancer cells. We have investigated the dielectric properties of Jurkat cells (a malignant human T-cell line) before and after exposure to either: 8 consecutive 1.1-kV/cm electroporation pulses of 100 μs, or 8 consecutive 20-kV/cm pulses of 300 ns, with a repetition rate of about 1 Hz. Measurement results show that conductivities of the cell suspensions increased significantly following microsecond or nanosecond exposure. Further analysis, based on the combination of a Maxwell-Wagner mixture model and a double shell cell model, shows increases in the plasma membrane conductivity, indicating that membrane poration has occurred. Significant changes in cytoplasm conductivity and nucleoplasm conductivity after nanosecond pulsed electric field exposure were also observed, indicating that nanosecond pulses had affected intracellular structures The induced changes were significantly different for different regimens, suggesting different membrane-charging and pore-forming mechanisms.