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FREQUENCY-DEPENDENT CHANGES IN GAP JUNCTION FUNCTION IN PRIMARY HEPATOCYTES
Citation:
Wang, X., D. E. House, J. Page, AND C F. Blackman. FREQUENCY-DEPENDENT CHANGES IN GAP JUNCTION FUNCTION IN PRIMARY HEPATOCYTES. Presented at Bioelectromagnetics Society Annual Meeting, St. Paul, MN, June 10-14, 2001.
Description:
FREQUENCY-DEPENDENT CHANGES IN GAP JUNCTION FUNCTION IN PRIMARY HEPATOCYTES. X. Wang1 *, D.E. Housel *, J. Page2, C.F. Blackmanl. 1 National Health and Environmental Effects Research Laboratory, USEPA, Research Triangle Park, North Carolina 27711 USA, 2Oakland, California USA
OBJECTIVE: We previously showed that gap junction communication (GJC) in mouse primary hepatocytes could be enhanced by treatment with physiological levels of melatonin. We also showed that this enhancement could be eliminated in a time dependent manner by exposure to AC/DC magnetic fields, selected by the ion parametric resonance (IPR) model tuned for Mg ion resonance. The objective of the presentation is to examine the frequency-dependence of this reduction in GJC in primary hepatocytes due to coincident melatonin and magnetic field exposures. METHODS: Primary hepatocytes, prepared from B6C3F1 male mice according to the method of Klaunig et al., were treated with 0.4 nM melatonin for 24 hours. Treated cells were then exposed to sinusoidal magnetic fields, 38.4 uT DC and parallel 40, 42.5, 45, 47.5 or 50-Hz AC at 24.4 uTrms, for selected time periods up to 3 hours. Following treatment, the cells were microinjected with Lucifer yellow dye and the percentage of nearest neighbor cells to which the dye transferred (dye coupling) was determined. RESULTS: The amount of dye coupling was reduced from 96% (sham treatment) to 80% under the 45-Hz magnetic field exposure condition, and that reduction reached maximal value by 1.5 hours and persisted there at later exposure times. Exposure at either 42.5 or 47.5 Hz caused a lesser reduction in GJC over the 3hr treatment, whereas exposure at 40 or 50 Hz caused very little or no change in GJC over the same exposure period. DISCUSSION: Connexin genes have recently been shown to display tumor suppression properties, presumably through the activity of their protein products which form gap junctions, allowing GJC between adjacent cells. One measure of GJC is the transfer of Lucifer yellow fluorescent dye among cells. Putative and known tumor promoting chemicals can reduce GJC, and it has been hypothesized that such reduction is a significant event in the tumor promotion process. We have shown that melatonin, a hormone with oncostatic properties, can enhance GJC, and that AC/DC magnetic fields tuned for resonance for Mg, according to predictions of the IPR model, can remove that GJC enhancement. In this presentation we show that another property predicted by the IPR model, that of frequency resonance, also occurs with a bandwidth previously observed for the effect of AC/DC magnetic fields, tuned for hydrogen ions, on neurite outgrowth in rat PC-12 cells. The time-dependent changes observed in GJC, due to the magnetic field exposure, are of a time scale that is consistent with plasma-membrane phenomenon involving second messenger systems for modulation. The ability of a physiological concentration of melatonin and of IPR-tuned magnetic fields to modulate GJC may provide a basis to begin molecular level studies of gap junction regulation, which could yield insight into tumor promotion or suppression mechanisms.
Authors supported by USEPA (CFB, DEH) and by DOE (CFB), IAG# DE-AI0194CE34007. JP was supported by Bechtel Corp. X. Wang was supported by a National Research Council Associateship. This abstract does not reflect EPA , NRC, or Bechtel Corporation policy.