Electromagnetic field stimulation of biosynthesis: Changes in c-myc transcript levels during continuous and intermittent exposures

We studied the effects of continuous and single limited exposures of HL60 cells to 60 Hz electromagnetic (EM) fields. Results showed an increase in transcript levels for c-myc peaks after 20 min of exposure, but the rate of return of this transcript to control levels is dependent upon whether the field is left on or turned off after 20 min. Turning off the field prolongs, by a factor of 3, the interval during which c-myc transcript levels remain elevated in response to EM field exposure. The effect of a second EM field stimulation on HL60 cells at some interval after an initial 20 min exposure was also examined. We found that the cells became refractory to a second stimulation at the same field amplitude, but that stimulation with a field of different amplitude (either higher or lower than the initial field) produced a restimulatory response.