THE ROLE OF TEMPORAL SENSING IN BIOELECTROMAGNETIC EFFECTS

Experiments were conducted to see whether the cellular response to ele ctromagnetic (EM) fields occurs through a detection process involving temporal sensing. L929 cells were exposed to 60 Hz magnetic fields and the enhancement of ornithine decarboxylase (ODC) activity was measure d to determine cellular response to the field. In one set of experimen ts, the field was turned alternately off and on at intervals of 0.1 to 50 s. For these experiments, field coherence was maintained by elimin ating the insertion of random time intervals upon switching. Intervals less than or equal to 1 s produced no enhancement of ODC activity, bu t fields switched at intervals greater than or equal to 10 s showed OD C activities that were enhanced by a factor of approximately 1.7. Thes e data indicate that it is the interval over which field parameters (e .g., amplitude or frequency) remain constant, rather than the interval over which the field is coherent, that is critical to cellular respon se to an EMF. In a second set of experiments, designed to determine ho w long it would take for cells to detect a change in field parameters, the field was interrupted for brief intervals (25-200 ms) once each s econd throughout exposure. In this situation, the extent of EMF-induce d ODC activity depended upon the duration of the interruption. Interru ptions greater than or equal to 100 ms were detected by the cell as sh own by elimination of field-induced enhancement of ODC. That two time constants (0.1 and 10 s) are involved in cellular EMF detection is con sistent with the temporal sensing process associated with bacterial ch emotaxis. By analogy with bacterial temporal sensing, cells would cont inuously sample and average an EM field over intervals of about 0.1 s (the ''averaging'' time), storing the averaged value in memory. The ce ll would compare the stored value with the current average, and respon d to the EM field only when field parameters remain constant over inte rvals of approximately 10 s (the ''memory'' time). (C) 1997 Wiley-Liss , Inc.