U. Friedrich et al., High efficiency electrotransfection with aluminum electrodes using microsecond controlled pulses, BIOELECTR B, 47(1), 1998, pp. 103-111
Electropermeabilization (electroporation) has been used widely for incorpor
ation of xenomolecules (up to the size of DNA) into eukaryotic cells withou
t loss of cellular functions. Frequently, low-cost equipment is used which
delivers exponentially decaying field pulses of low intensity and milliseco
nd duration time. This together with the use of disposable cuvettes equippe
d with aluminum plate electrodes can considerably reduce the survival of th
e cells and the incorporation of xenomolecules because of the detrimental s
ide effects of long-duration pulses and the toxicity of Al3+ ions on permea
bilized cells. Atomic absorption spectroscopy showed that substantial amoun
ts of Al3+-ions (up to 1 mM) were solubilized from the electrodes upon puls
ing. Solubilization of Al3+-ions occurred because of the changes of the pH
close to the electrodes induced by electrolysis of water. The local pH-chan
ges could be visualized by the addition of pH-indicators together with agar
ose to the pulse medium. In contrast, when using short pulses of 40 mu s to
100 mu s duration, small amounts of Al3+-ions were only solubilized from t
he electrodes upon pulsing. Electroinjection of the plasmid pEGFP-Cl (encod
ing for Enhanced Green Fluorescence Protein) in four different (murine and
human) cell lines showed that relatively high survival rates of cells and s
pecies-specific transfection yields (of up to 50-70% as measured by FAGS an
alysis) could be obtained by using aluminum electrodes provided that short-
duration pulses were applied. These yields were in the range obtained by us
ing stainless steel electrodes. The required short-duration pulses and fiel
d strengths for field-induced incorporation of pEGFP-Cl were achieved using
a novel power supply (maximum output voltage of 1.2 kV, pulse durations be
tween 15 mu s and 500 mu s) in combination with strongly hypo-osmolar pulse
media. (C) 1998 Elsevier Science S.A. All rights reserved.