Experimental study and mechanism analysis on cell electroporation due to low-intensity transient electromagnetic pulses

Liu CJ, Wang BY, Zhang H, Wang ZS, Chen MF

Chin Science Bulletin 44:1157-1161, 1999

(in Chinese)

Using scanning electron microscope. this was the first proof of electroporation due to low-intensity electric pulses. EMP with 100ns duration at 300Hz repeat frequency and 2 kV/m were used. The BTEM Cell was used to simulate the free space radiation condition.

Chick erythrocytes were put into the BTEM Cell to accept irradiation for 20, 40, 60, 80 and 100 minutes, respectively. One group of chick erythrocyte was served as control. A scanning electronic microscope was used to observe chick erythrocyte electroporation.

The results showed that the incidence of electroporation was more than 2% with the pores from 20 - 500 nanometers, which occurred in all exposure groups with the different exposure duration. The highest incidence (near 3%) appeared in the 100 minutes exposure group; no electroporation was observed in the control group.

The processes of the cell membrane electroporation showed that the protuberance formed by cytoplasm before the membrane pore appeared; then the cytoplasm was blowing from the cell to form a pore on membrane; and the depression appeared when the membrane was healing.

Under the same irradiation condition, the erythrocyte fusion in chick-chick, rabbit-rabbit, and chick-rabbit was also observed. The incidence of cell fusion was less than 5â

The authors indicated that the induced maximum transmembrane potential by the electric pulses is 18 mV which is less than half of the cell resting potential 70 mV. The electric breakdown threshold of cell membrane is 500 mV. So low-intensity electric field can not directly lead to cell membrane electroporation by the electric breakdown. On the cell membrane many very small transient pores generate and decay spontaneously due to the random thermal motion. According to the weaveís mode of interaction between electric field and cell membrane, and the increase of transmembrane potential can enlarge the small pores on membrane (J.Weave), the authors suggested that under the repeated action of pulses, the small pores became larger and larger. When the small pores were large enough, many small molecules and ions can cross the membrane and enter the cell leading to cell swelling. Surface tension generated by the swelling membrane made the small pores larger and larger until a pore was presented and cytoplasm was blowing outside to balance the osmotic pressure. Since part of the cytoplasm was ejected, there would be a depression after the pore healed.