Apoptosis induction effects of steep pulsed electric fields (SPEF) on human liver cancer cell SMMC-7721 in vitro

To research the apoptosis effects of steep pulsed electric fields (SPEF) on human liver cancer cell SMMC-7721 in vitro, this paper studied phosphatidylserine (PS) externalization detection utilizing flow cytometry, real-time change of mitochondrial transmembrane potential (DeltaPsi_m) using confocal laser scanning microscope (CLSM) and DNA fragmentation assay by agarose gel electrophoresis. The experiment results by flow cytometry showed that musSPEF (SPEF with electric field intensity of 200 V/cm and duration of 1.3 mus) effectively (P<0.05) induced PS externalization but nsSPEF (SPEF with electric field intensity of 600 V/cm and duration of 100 ns) did not (P>0.05). On the contrary, nsSPEF induced DeltaPsi_m decrease and DNA fragmentation more notably than musSPEF. These results indicate that SPEF can distinctly induce apoptosis and the effects are electric field intensity/pulse duration-dependent. Theoretically calculation showed that temperature increase of cell solutions for treated groups exposed to SPEF was less than 1.3 K without regard to heat dissipation. Multi-shelled dielectric cell model and frequency spectrum analysis showed that musSPEF contained abundant low frequency components which mainly acted on plasma membrane, whereas nsSPEF contained plentiful high frequency components which permeated plasma membrane and mainly affected on intracellular organelle.