Action spectra and mechanisms of (in) efficiency of bipolar electric pulses at electroporation

Control of the Electroporation Efficiency of Nanosecond Pulses by Swinging the Electric Field Vector Direction

“…Maximum cancellation was expectedly observed at the 180° vector change, reducing YP uptake compared to single-pulse trains 2-fold at 1 Hz and as much as 20-fold at 833 kHz. Stronger cancellation at sub-MHz frequencies was consistent with our previous report using bipolar pulses [ 17 ]. Cancellation weakened as the angle was reduced, and at about 160° (1 Hz) or 130° (833 kHz), the effects of paired-pulse trains became the same as those of single-pulse ones.…”

“…Consistently with the measurements in Figure 2 , co- and cross-directional pulses at 1 Hz had the same electroporation efficiency ( Figure 3 ). Increasing the pulse frequency to 770 kHz enhanced electroporation by the co-directional pulses because of the temporal summation of the induced membrane potential [ 17 , 26 , 27 , 28 ]. Interestingly, charging two different regions of the cell membrane did not cause summation, making cross-directional pulses at 770 kHz just as effective as at 1 Hz.…”

“…The effect of direction change becomes more complex when EP duration is decreased into the nanosecond and short microsecond range. Applying a second nanosecond EP (nsEP) in the direction opposite to a preceding first nsEP inhibits (or “cancels”) the anticipated effects of the first nsEP [ 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. As a result, the electroporation and electrostimulation efficiency of a pair of opposite-direction pulses is smaller than of the first nsEP alone, despite delivering more energy.…”

“…The biophysical mechanisms of this “bipolar cancellation” effect are not fully understood despite extensive research. It has recently become clear that the bipolar cancellations of neurostimulation and electroporation have different dependences on pulse parameters and are likely caused by different mechanisms; there may also be a difference in cancellation mechanisms for electroporation by the shortest nsEPs (a few nanoseconds) and EPs in the range of hundreds of nanoseconds to microseconds [ 17 ].…”

“…We applied several pulse pairs so that the electric field vector was alternating (“swinging”) between two directions. The measurements were performed both at 1 Hz and at a high repetition rate of 833 kHz, which markedly enhanced cancellation for the 600 + 600 ns pulse pairs [ 17 ]. The experiments revealed a remarkably strong dependence of electroporation efficiency on the angle, especially for the high-rate pulse trains.…”