Control by electrical parameters of short- and long-term cell death resulting from electropermeabilization of Chinese hamster ovary cells.

Chinese hamster ovary (CHO) cells were pulsed by using brief intense square-wave electric field pulses. The electrical treatment induced a transient local permeabilization of the cell membrane. The growth of CHO cells after electropulsation in an iso-osmotic pulsing buffer with low ionic content was measured. Parallel experiments evaluated cell death which took place in the minute range after electropulsation (short-term death) and the cell death upon 24 h (long-term death). Short-term cell death was defined as the case of cells with membrane still permeable to Direct-blue at 15 min after electropulsation. It was observed only under stringent pulsing conditions where electropermeabilization of the two sides of the cell was triggered. The long-term cell death, i.e., the inability of some pulsed cells to grow was observed as soon as permeabilization had been triggered. The higher the permeabilization level of the cell population was, the higher the long-term cell death level was. The cell death was linearly related to the reciprocal of the electric field intensity, i.e., to the fraction of the membrane area electrically brought to the permeable state. From this work, it appeared that for high levels of permeabilization of a cell suspension, best cell survivals were obtained if limited alterations were triggered over a large area of the plasma membrane (single pulse with high intensity) than if a small area of the membrane was strongly altered (repetitive pulses with small intensity). The highest yield of viable permeabilized cells was achieved when using one single pulse of duration up to 1 ms.