Abstract
The present study compared electroporation efficiency of bipolar and unipolar nanosecond electric field oscillations (NEFO). Bipolar NEFO was a damped sine wave with 140 ns first phase duration at 50% height; the peak amplitude of phases 2–4 decreased to 35%, 12%, and 7% of the first phase. This waveform was rectified to produce unipolar NEFO by cutting off phases 2 and 4. Membrane permeabilization was quantified in CHO and GH3 cells by uptake of a membrane integrity marker dye YO-PRO-1 (YP) and by the membrane conductance increase measured by patch clamp. For treatments with 1–20 unipolar NEFO, at 9.6–24 kV/cm, 10 Hz, the rate and amount of YP uptake were consistently 2-3-fold higher than after bipolar NEFO treatments, despite delivering less energy. However, the threshold amplitude was about 7 kV/cm for both NEFO waveforms. A single 14.4 kV/cm unipolar NEFO caused a 1.5–2 times greater increase in membrane conductance (p < 0.05) than bipolar NEFO, along with a longer and less frequent recovery. The lower efficiency of bipolar NEFO was preserved in Ca2+-free conditions and thus cannot be explained by the reversal of electrophoretic flows of Ca2+. Instead, the data indicate that the electric field polarity reversals reduced the pore yield.
Highlights
The composition of solutions utilized in different experiments is described in respective sections below
We observed that the second phase of only 35% of the first one is sufficient to partially cancel the effect of the first phase. It remains to be studied how the degree of cancellation depends on the ratio of the first and second phases
Ca2+ entry will determine many downstream effects of electroporation[32,53,54] and the reversal of the electric field may potentially reduce the net Ca2+ uptake[41]; here we report a direct and Ca2+-independent impact of the electric field reversal on the membrane permeabilization
Summary
The composition of solutions utilized in different experiments is described in respective sections below. Of the bipolar cancellation phenomenon which was described earlier for rectangular-shaped nanosecond pulses with the same amplitude of positive and negative phases[33]. We established that the bipolar cancellation phenomenon does not result from the reduced electrophoresis-driven Ca2+ entry into cells[41].
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