Non-thermal and transient thermal effects of burst 100 MHz sinusoidal electric fields on apoptotic activity in HeLa cells

This paper describes non-thermal and transient thermal effects of burst 100 MHz, 100 kV/m sinusoidal electric fields on the apoptotic activity in cultured HeLa cells. Two kinds of pulsing sequences, 50 0.2 ms-long pulses with 2 s intervals and a single 10 ms-long pulse, were used for the non-thermal and the superposition of transient thermal shock on the non-thermal loading, respectively. The externalization of phosphatidylserine as an indication of apoptosis activity and the membrane defect regarded as cell death were detected by using molecular probes annexin V-FITC and propidium iodide, respectively. As a result of the statistical analysis of approximately 4000 cells using a flow cytometer, most of the cells survives for at least 2 h after the exposure, and apoptotic cell number was gradually increased in the range of hours. The 10 ms-long pulsing, which causes the transient temperature change of 25°C, induced apoptosis to more HeLa cells than the non-thermal 0.2 ms-long pulsing. The superposition of the transient thermal shock on the non-thermal loading produced by the IBSEF pulsing can be a new biological stress to enhance the conventional nonthermal effect.