Release of mediators by DMSO-differentiated HL-60 cells exposed to electric interferential current and the requirement of biochemical prestimulation

Abstract

Purpose : Controversial results have been obtained with respect to the influence of biochemical prestimulation upon the action of electromagnetic fields on mammalian cells. Examined in detail has been the influence of a modulated low-frequency (interferential) current upon the release of four mediators by DMSO-differentiated HL-60 cells with and without prestimulation by the chemotactic peptide N -formyl-methionyl-leucyl-phenylalanine (fMLP). Materials and methods : Human promyelocytes (HL-60) cells differentiated to granulocytes by dimethylsulphoxide were exposed to a so-called interferential current (IFC) in a suspension culture. The influence of IFC treatment, an amplitude-modulated 4000 Hz current used in therapeutic applications, on the release of prostaglandine E 2 (PGE 2) , leukotriene B 4 (LTB 4) , thromboxane B 2 (TXB 2) and interleukin 8 (IL-8) was investigated. Effects of a static magnetic field were also studied. Results : In no case were significant differences between exposed and sham-exposed samples observed after 15 min exposure to selected modulation frequencies (0-125Hz, 250 μ A cm -2) . Therefore, the influence of prestimulation with different concentrations of fMLP on the release of the four mediators was investigated. fMLP alone enhanced the release of PGE 2, LTB 4, TXB 2 and IL-8 with half of the maximum (ED 50) effective concentration of ~10nM. Prestimulation with various concentrations of fMLP and subsequent exposure to IFC 125Hz (15 min, 250 μ A cm -2) had no effect at low or high concentrations of fMLP, while in the middle range of concentration of ~100 pM fMLP a significant enhancement of PGE 2, LTB 4 and IL-8 was observed. This synergistic effect of fMLP and IFC was examined in detail in prestimulated cells (100pM fMLP) by varying the exposure time, current density and modulation frequency in the range 0-50 Hz. Window effects for the release of PGE 2, LTB 4 and IL-8 were obtained for exposure time, current density and modulation frequency whereas, in the release of TXB 2, no field effect was detected. Conclusion : The study has demonstrated the synergistic action of chemical stimulation and electric current exposure, and the existence of windows for cellular activation status, exposure time, current density and modulation frequency.