Electron Paramagnetic Resonance Study of Pulsed Electric Field-Assisted Internalization of Spin Probes into Yeast Cells

Efficient internalization of chemical entities into cells across the plasma membrane barrier is crucial for most biomedical applications. Among the physical factors that can enhance the delivery of active substances, the electric field plays an important role. In our experiments, electron paramagnetic resonance (EPR) spectroscopy was used to monitor the process of electric field-assisted endocytosis of a spin probe TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) into yeast cells (Saccharomyces cerevisiae). It was found that a long train of low-amplitude voltage pulses (0.5–20 Vpp) can affect the uptake of nitroxide by cells. In addition to the pulse amplitude, the key parameters influencing the internalization process are: frequency, duty cycle and time of exposure to the electric field. The sodium chloride content in the medium in which the cells are suspended is also of great importance. For higher salt concentrations, starting from 3.5% w/w, a significant decrease in cell survival was observed after exposure to an electrical stimulus, which also translated into a decreasing spin probe uptake. Our studies confirm the usefulness of EPR spectroscopy in the study of internalization processes and show that the parameters of electric field pulses and the environmental salinity have a significant impact on the course of electroendocytosis.