Evidences for membrane electroporation during application of nanoseconds electrical pulses

Summary form only given. It was suggested that high intensity (>100 kV/cm) short duration (ns) electrical pulses could affect the intracellular structures of mammalian cells without adversely affecting the outer cell membrane by electroporation. In order to demonstrate this on microorganisms with and without internal structures, we have studied the effect induced by short electrical pulses (25-600 ns) on membrane integrity of Saccharomyces cerevisiae (backer yeast) and Pseudomonas putida (bacteria). Cells were stained after pulse treatment with BacLight (Syto9 and propidium iodite, PI) and counted using an epifluorescence microscope. For comparison with viability studies, the cells were staining with FUN1 (yeast) CTC (bacteria) and additional plating the sample on culture media. A Blumlein generator provided square wave voltage pulses of 25 ns to the commercial (BTX) treatment chambers. Longer high voltage pulses (100-600 ns) were produced using a line generator. Viable cells, treated using short pulses, were swollen; whereas inactive cells showed almost a permeable membrane, indicated by PI. The inactivation rates of yeast and bacteria were of the same order of magnitude and comparable with those obtained by other studies. The rates of cells stained with BacLight were related to the rates obtained by counting the metabolically active cells stained with FUN1 or CTC. We found out that inactivation rates of yeast and bacteria only depend on the treatment duration (t/sub pulse//spl middot/n) and on the product of square field intensity and treatment duration (E/sup 2//spl middot/t/sub pulse//spl middot/n). These results support the assumption that the main effect of short electrical pulses (ns - range) is the electroporation of the outer cell membrane.