Frequency dependence of electroporation of mammalian cells by pulsed high power radiofrequency and ultrawideband radiation

Abstract

Summary form only given. A series of experiments has been performed to determine the effectiveness of radiofrequency (RF) and ultrawideband electric fields for electroporation of cells, since these fields can be launched or focused by a waveguide or antenna. In a first series of experiments at moderate electric fields, we compared the electroporation response of electrically excitable and non-excitable cells with two cell lines: the N1E-115 murine neuroblastoma and the COS-1 African green monkey kidney fibroblast. Four electric field modalities were used; each exposure consisted of a train of five pulses at 1-s intervals. Square (DC) pulses (1-ms) were used for comparison to the RF-modulated fields. Bursts (2-ms) of unipolar RF at 25 kHz, bipolar RF at 20 kHz, and bipolar RF at 13.56 MHz were applied to cells to observe the frequency dependence of the electroporation response. Applied electric fields ranged from 0-2.0 kV/cm. Electroporation and cell killing by DC pulses and unipolar RF pulses were consistent with earlier results. For field strengths up to 2 kV/cm, 2-ms unipolar RF bursts produced both less killing and less permeabilization than 1-ms DC pulses. The reduced killing of the RF bursts resulted in higher electroporation yields for these exposures at some electric field strengths. For bipolar RF bursts (no DC offset), 2-ms bursts had no measurable effect on cell killing or permeabilization at field strengths up to 1.5 kV/cm at 20 kHz or 13.56 MHz. The most recent experiments at UM have tested the effects of bipolar, pulsed, high electric fields (45-180 kV/cm) on electroporation and apoptosis of Jurkat T lymphocytes. The electrical pulses have fast-risetime (<2 ns) and in a mismatched configuration exhibit a bipolar-pulse train of some 70 ns total duration, with spectral content up to 1.2 GHz. Single pulses as well as trains of up to 200 pulses at 1 Hz repetition frequency were applied. At peak electric fields of 45-180 kV/cm, single pulses induce apoptosis, whereas multiple pulses (5-200) kill most cells.