Real‐time measurement of cytosolic free calcium concentration in DEM‐treated HL‐60 cells during static magnetic field exposure and activation by ATP

Abstract

This study investigated whether glutathione depletion affected the sensitivity of HL-60 cells to static magnetic fields. The effect of Diethylmaleate (DEM) on static magnetic field induced changes in cytosolic free calcium concentration ([Ca(2+)](c)) was examined. Cells were loaded with a fluorescent dye and exposed to a uniform static magnetic field at a strength of 0 mT (sham) or 100 mT. [Ca(2+)](c) was monitored during field and sham exposure using a ratiometric fluorescence spectroscopy system. Cells were activated by the addition of ATP. Metrics extracted from the [Ca(2+)](c) time series included: average [Ca(2+)](c) during the Pre-Field and Field Conditions, peak [Ca(2+)](c) following ATP activation and the full width at half maximum (FWHM) of the peak ATP response. Comparison of each calcium metric between the sham and 100 mT experiments revealed the following results: average [Ca(2+)](c) measured during the Field condition was 53 +/- 2 nM and 58 +/- 2 nM for sham and 100 mT groups, respectively. Average FWHM was 51 +/- 3 s and 54 +/- 3 s for sham and 100 mT groups, respectively. An effect of experimental order on the peak [Ca(2+)](c) response to ATP in sham/sham experiments complicated the statistical analysis and did not allow pooling of the first and second order experiments. No statistically significant difference between the sham and 100 mT groups was observed for any of the calcium metrics. These data suggested that manipulation of free radical buffering capacity in HL-60 cells did not affect the sensitivity of the cells to a 100 mT static magnetic field.

The effect of 100 mT SMF on activation of the hsp70 promoter in a heat shock/luciferase reporter system

“…The average water bath temperature was approximately 37°C at basal levels, and was increased to 42°C at t = 1,800 s, in two groups of experiments. The water bath temperature remained elevated until t = 3,600 s. During the 100 mT SMF exposure, the apparent bath temperature increased by approximately 0.1°C, which was attributed to electronic interference of the magnet with the thermistor as described previously [Rozanski et al, 2009]. After the SMF was returned to 0 mT, the bath temperature reading returned to 37°C or 42°C almost immediately depending on the heat condition.…”

“…The data from this study was also not corrupted by potential artifacts from SMF‐related changes in water bath temperature. No direct influence on water bath temperature was observed before, during or after the application of current to the electromagnet either for the sham or 100 mT experimental runs, as described previously [Rozanski et al, 2009].…”

“…1). As described in detail elsewhere [Belton et al, 2008; Rozanski et al, 2009] a toroidal electromagnet (15 mm pole gap, 16 AWG copper magnet wire, Arnold Engineering) (M in Fig. 1) was held within the water bath (kept at 37 ± 0.1°C or 42 ± 0.1°C) by temperature controlled circulating water.…”

Purinergic signalling and cancer

“…ATP induced apoptotic cell death of both HL-60 and F-36P leukaemia cell lines [456]. Static magnetic field exposure of HL-60 cells increased the increase in [Ca 2+ ] i produced by ATP [457,458]. A 3 receptor agonists were shown to inhibit proliferation and induce apoptosis of HL-60 leukaemia cells [459,460].…”

Gaps in Knowledge Relevant to the “Guidelines for Limiting Exposure to Time-Varying Electric and Magnetic Fields (1 Hz–100 kHz)”

“…Several studies using different types of cancer cells have shown contradictory effects on oxidative stress. No effect was found in HL-60 cells exposured to 100 mT for 13 min by Rozanski et al (2008), while a 2 h exposure to 6 mT increased oxidative stress in U937 monocytic tumour cells (De Nicola et al 2006).…”