Measurement of Electric Modification of Cell Suspension Conductivity During Treatment

High-intensity electric pulses (EPs) alter the mechanical structure of mammalian cells by creating small pores in the plasma membrane 1. One can correlate these EP induced structural changes to changes in electrical properties 2, 3. One electrical characterization technique is time domain dielectric spectroscopy (TDDS), in which one applies low intensity EP to a cell suspension and measures the reflected signal. From this, one can extract the conductivity and permittivity of the plasma membrane, cytoplasm, nuclear envelope, and nucleoplasm in cells by using a two-shell model 2, 3. However, TDDS uses sensitive equipment that prohibits measuring the changes of these properties during a high-intensity EP. In this study, we measure the changes in cell suspension conductivity in real time to elucidate ion transport during EPs. We fix EP application at three different energy densities for three cell media of different conductivity and ion concentration and pulse durations of 60 ns and 300 ns. The conductivity increased during the pulse, indicating ion motion from the cell to the extracellular medium. While similar to the increased conductivity observed by TDDS [2], those measurements occurred greater than one minute after exposure, meaning that diffusion could contribute while the measurements during the EP would only consider electrophoresis. We use a mathematical model 4 coupling the asymptotic Smoluchowski representation of EP induced pore formation with the Nernst-Planck model for ion motion to predict ion motion for the EP parameters studied here to elucidate the contributions of electrophoresis and diffusion. The implications for the mechanisms involved in EP-induced electropermeabilization and ion transport will be discussed.