Response of Mammalian cells to non-thermal intense narrowband pulsed electric fields

This paper describes the biological effect of intense pulse electric field from the frequency point of view. A pulse-modulated sinusoidal wave as the A narrowband pulsed electric field (nbPEF) allows us to deliver a non-thermal, intense and well-defined electric field in terms of frequency, field strength and deposition energy to biological systems. 10 μs long sinusoidal electric fields with a frequency range between 0.1 and 100 MHz and field strengths of up to 10 kV/cm were applied to HeLa or HeLaS3 cells, which were subsequently analyzed in terms of the morphology and the Ca²⁺ response. The field with the frequency below a few MHz immediately causes blebs in the external field direction, whereas the morphology does not change apparently in the case of the frequency more than 10 MHz. The intracellular Ca²⁺ concentration rapidly increased after the exposure to the low frequency field and subsequently decayed exponentially within hundreds of seconds. Inversely, for the high frequency fields, the Ca²⁺ concentration did not change for seconds after the pulse, but increased gradually in tens to hundreds of seconds. When the Ca²⁺ channel on the plasma membrane was inhibited, the delayed Ca²⁺ uptake was suppressed. Our experiment shows that the possibility to activate or impair function of membrane proteins physically by using nbPEF without significant defects of the plasma membrane.

I. Introduction

Biological effects of intense pulsed electric fields (PEFs) have been reported over the past three decades. Neumann firstly reported in 1972 permeability changes induced by PEFs in membrane [1]. PEFs with a pulse length of longer than are generally used for electroporation because the cell membrane acts as a capacitor and has to be charged to a sufficient voltage to cause membrane defects [2]. Schoenbach et al have started using nanosecond pulsed electric fields (nsPEFs) and reported their effects on various kinds of mammalian cells over the past decade [3]. Application of nsPEFs to biological cells results in intracellular effects with the intense electric field inside the cell seemingly adding a new stress to the internal biological system which will potentially be used for biotechnology and medical treatment.