Reversible electropermeabilization of mammalian cells by high-intensity, ultra-short pulses of submicrosecond duration

Mouse myeloma cells were electropermeabilized by single square-wave electri c pulses with amplitudes of up to similar to 150 kV/cm and durations of 10- 100 nsec. The effects of the field intensity, pulse duration and medium con ductivity on cell viability and field-induced uptake of molecules were anal yzed by quantitative flow cytometry using the membrane-impermeable fluoresc ent dye propidium iodide as indicator molecule. Despite the extremely large field strengths, the majority of cells survived the exposure to ultra-shor t field pulses. The electrically induced dye uptake increased markedly with decreasing conductivity of the suspending medium. We assigned this phenome non to the transient electrode-formation (stretching) force that assumes it s maximum value if cells are suspended in low-conductivity media, i.e., if the external conductivity sigma (e) is smaller than that of the cytosol sig ma (i). The stretching force vanishes when sigma (e) is equal to or larger than sigma (i). Due to their capability of delivering extremely large elect ric fields, the pulse power systems used here appear to be a promising tool for the electropermeabilization of very small cells and vesicles (includin g intracellular organelles, liposomes, etc.).