Non-thermal and transient thermal effects of pulsed electric fields on HeLa cells

The transient thermal shock (TTS) is instantaneous temperature change, more than ten degrees within seconds, caused by the pulsed electric fields. The famous thermal effect is heat shock (42-45°C for more than 10 min), we call it stationary heat shock (SHS) in this paper. However, the temperature history of TTS is quite different from SHS. Living organ have never been exposed the rapid temperature change like TTS, TTS may provide a novel biological stress. Here, we compare the effect of these three agents, the field-induced TTS, the non-thermal (NTFE) 100 MHz burst fields effects and the SHS. Instantaneous temperature of cell suspending media during the pulse application was monitored by a fast radiation thermometer. The electric field ranges were 0.25, 1, 4 kV/cm and the temperature ranged from 25 to 85°C, respectively. The viability was detected by using propidium iodide (PI) and statistically evaluated by using a flow cytometer. In all electrics fields, the percentage of PI positive cells was increased by temperature-dependently. Moreover, in all electric fields, the percentage of PI positive cells was increased by time-dependently.