Effects Of Power Frequency Magnetic Fields On GJIC Of Astrocytes

Background and Objective There have been arguments so far about thebiological effects of power frequency magnetic fields(PFMFs),particularly about the influence of PFMFs on cancer development.Fewstudies of possible tumor promoting effects of PFMFs on brain have beenreported.EpidemiologicaI studies suggested that A link increased risk ofbrain tumor and exposure of PFMFs was disputed. Laboratory studiesrevealed that PFMFs could induce an increase in DNA single and doublestrand breaks,in DNA-DNA and DNA-protein crosslinks of brain cells.Recently,the disruption of gap junction intercellular communication(GJIC)was considered as an important index for determination of suspiciouscancer promoters.The present experiment was to study whether PFMFscould act as brain tumor promoter or co-promoter with other promotersuch as Tetradedecanoyl phorbol acetate(TPA),through exploring thepossible effects of 50Hz sinusoidaI magnetic fields on GJIC in astrocytesof cerebrum of SD rats.Materials and Methods l .Groups:(l )sham-exposed controI group;(2)PFMPs at flux density 0.8tnT group;(3)PFMFs at flux density l .6mTgroup;(4)TPA group;(5)PFMFs at flux density 0.8mT combined with TPAgroup;(6)PFMPs at flux density l .6mT combined with TPA group.2 .Culture and identifycation of astrocytes:Astrocytes which wereobtained from cerebrum of SD rats(l -3 days old) were primary culturedfor 9 days,then subcultured one time fOr 6 days.More than 98% of thecells were identified as confluent astrocytes by SP immunohistorychemical staining antibodies directed against glial fibrillary acidicprotein(GFAP). 3 .Treatment of astrocytes:Astrocytes in TPA groupwere exposed to TPA at 3ng/ml concentration for lhr.The exposureduration for PFMFs at flux density of 0.8mT or l.6mT was 24 hrs.Astrocytes in PFMFs combined with TPA groups were exposed to PFMFsat flux density 0.8 or l.6mT for 23h,then exposed to PFMFs and TPA(3ng/ml) for lh at the Iast lh. 4.Assay of GJIC by fluorescencerecovery after photobleaching (FRAP):After treatments,cells were dyedby 6-carboxyfluorescein diacetate,then GJIC was measured by FRAPanalysis with a laser-scanning con focal microscope.At last take confOcalimages,measure the fluorescence intensity in the bleached and unbIeachedcells,and plot a function of tbe fluorescence intensity(independentvariabIe) in the bleached and unbleached ceIIs to time(dependentvariable). 5.Statistical analysis:Statistical analysis were perfOrmedusing the Kruskal and Wallis's - test and Kendall's rank correlationtest.And Q <0.05 suggested significant diffenrence.Rults l .At 0min after photobleaching,comparative fluorescenceintensity recovery percentage(CFIRP) of all groups were 0%. Withscanning time prolonging,CFIRP came to increase.At l0min afterphotobIeaching,CFIRP of controI group basicaIly restored to theprephotobleaching level.So fluorescence intensity of l0-min-after-photobleaching was chosen to statistical analysis.With scanning timepro longing,comp arative fluorescence intensity recovery rate(CFIRR) ofall groups came to descend. 2.TPA,a well known intense cancerpromoter,could suppress GJIC in many kinds of cells.The effect of TPAon GJIC was dependent on the concentration and duration of exposure.Based on literatures,the present experiment studied effect of TPA on GJICat 3ng/ml concentration for l h.The result showed that TPA at 3ng/mlconcentration could obviously inhibit GJIC of astrocytes(CFIRRc..t,.l:9.74,CFIRRTPA=4'53, H= l2.084, P=0.00l ). 3 .CFIRR of control,PFMFsat flux density 0.8mT,PFMFs at flux density l .6mT groups respectivelywere 9.74,8.25,6.68.PFMFs at flux density 0.8 or l .6mT could not inhibitGJIC of astrocytes alone(H=4. l24,p=0. l27,vs control).But there were' signitricant inverse correlation between PFMFs intensity and suppressionof GJIC(T =-0. l 80 l P=0.032),indicating that with PFMFs intensity(within0- l .6mT) increasing,the inhibition of PFMFs on GJIC showed...