Cell membrane electropermeabilization by symmetrical bipolar rectangular pulses - Part II. Reduced electrolytic contamination

The paper presents a comparative study of the contamination of a cell suspe nsion by ions released from aluminum cuvettes (Al3+) and stainless steel el ectrodes (Fe2+/Fe3+) during cell membrane electropermeabilization by unipol ar and by symmetrical bipolar rectangular electric pulses. A single pulse a nd a train of eight pulses were delivered to electrodes at a 2-mm distance, with 100-mus and 1-ms pulse durations, and amplitudes ranging from 0 to 40 0 V for unipolar, and from 0 to 280 V for bipolar pulses. We found that the released concentrations of Al3+ and Fe2+/Fe3+ were always more than one or der of magnitude lower with bipolar pulses than with unipolar pulses of the same amplitude and duration. We then investigated the viability of DC-3F c ells after 1 h of incubation in the medium containing different concentrati ons of Al3+ or Fe2+/Fe3+ within the range of measured released concentratio ns (up to 2.5 mM for both ions), thus separating the effects of electrolyti c contamination from the effects of electropermeabilization itself. For Fe2 +/Fe3+, loss Of cell viability became significant at concentrations above 1 .5 mM, while for Al3+, no effect on cell survival was detected within the i nvestigated range. Still, reports on the biochemical effects of released Al 3+ also suggest that with aluminum cuvettes, electrolytic contamination can be detrimental. Our study shows that electrolytic contamination and its de trimental effects can be largely reduced with no loss in efficiency of elec tropermeabilization, if bipolar rectangular pulses of the same amplitude an d duration are used instead of the commonly applied unipolar pulses. (C) 20 01 Elsevier Science B.V. All rights reserved.