Citation:

TRILLO, A., A. UBEDA, S. G. BENANE, D. E. HOUSE, AND C. F. BLACKMAN. INFLUENCE OF DIFFERENT INCUBATOR MODELS ON MAGNETIC FIELD-INDUCED CHANGES IN NEURITE OUTGROWTH IN PC-12 CELLS. Presented at Bioelectromagnetics Society and the European BioElectromagnetic Association, Dublin, IRELAND, June 19 - 24, 2005.

Description:

OBJECTIVE: Devise a method to standardize responses of cells to MF-exposure in different incubator environments. METHODS: We compared the cell responses to generated MF in a standard cell-culture incubator (Forma, model #3158) with cell responses to the same exposure when a mu-metal box is in the incubator to shield the cells from EMF generated outside the box. A standard assay of neurite outgrowth (NO) from NGF-stimulated, primed PC-12 cells was used to explore the effects of 23 hours of exposure to magnetic fields (e.g., Blackman et al., 1994). The cells were exposed to a 45-Hz, ac, vertical magnetic field (Bac) over the flux density range of 12.0 - 31.0 mGrms [1.20-3.10 microTrms]. The Bac was parallel to a do MF of 29.7 mG [2.97 microT], with a perpendicular dc MF < 2.0 mG [0.20 microT]. These MF exposure conditions are predicted by the IPR model (Blanchard and Blackman, 1994) to produce the maximal reduction in NO under resonance conditions for hydrogen ions. Exposures of the cells to MF were performed under two conditions: with and without a mu-metal box in the incubator. These results were compared to those reported for similar exposures (Trillo et al., 1996; Blackman et al., 1999) using an older incubator (Forma, model #3156). RESULTS: The experimental results using the model #3158 incubator showed the expected U-shaped inhibitory response function with a peak of no inhibition at the general center of the response (Trillo et al., 1996). However, the ac MF flux density for the center of the response was shifted from a 2Bacpk/(Bdc) value of 1.70 (seen using the model #3156 incubator) to 2.12, and the response shape was distorted at higher values. When the mu-metal box was in the model #3158 incubator, the cell response returned to the original values observed using the older incubator (model #3156). DISCUSSION: We report that different models of a manufacturer's incubators can alter some cell responses to MF. One major distinction between the two incubator models we tested is the circuitry used to maintain a given temperature. In the older incubator, Forma model #3156, the heater current was either on or off to maintain temperature. In the newer incubator, Forma model #3158, a proportional heater circuit clips the 60-Hz sine wave into on-off segments that change as the temperature approaches the set point. A clipped sine wave could introduce higher frequency fields to the incubator chamber. Although the cause and implications of this result were not pursued further, a likely explanation for our results is that the additional EMF introduced by the proportional heating circuit interfered with the cell responses to the low-intensity ac MF we used. It should be noted that there was no detectable difference in cell response between the two incubator types when approximately 10-fold higher-intensity ac MF were used (e.g., Blackman et al., 1994, 1996). Our results show the mu-metal box provided satisfactory shielding from the causative agent, presumably the proportional heater circuit. This report is a warning for scientists to avoid additional sources of EMF in exposure systems because any results could be hard to interpret and to be duplicated elsewhere.

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