EMPIRICAL-TEST OF AN ION PARAMETRIC RESONANCE MODEL FOR MAGNETIC-FIELD INTERACTIONS WITH PC-12 CELLS

A companion paper describes a predictive ion parametric resonance (IPR ) model of magnetic field interactions with biological systems based o n a selective relation between the ratio of the flux density of the st atic magnetic field to the AC magnetic field and the charge-to-mass ra tio of ions of biological relevance. Previous studies demonstrated tha t nerve growth factor (NGF)-stimulated neurite outgrowth (NO) in PC-12 cells can be inhibited by exposure to magnetic fields as a function o f either magnetic field flux density or AC magnetic field frequency. T he present work examines whether the PC-12 cell response to magnetic f ields is consistent with the quasiperiodic, resonance-based prediction s of the IPR model. We tested changes in each of the experimentally co ntrollable variables [flux densities of the parallel components of the AC magnetic field (B-ac) and the static magnetic field (B-dc) and the frequency of the AC magnetic field] over a range of exposure conditio ns sufficient to determine whether the IPR model is applicable. A mult iple coil exposure system independently controlled each of these criti cal quantities. The perpendicular static magnetic field was controlled to less than 2 mG for air tests. The first set of tests examined the NO response in cells exposed to 45 Hz B-ac from 77 to 468 mG(rms) at a B-dc Of 366 mG. Next, we examined an off-resonance condition using 20 mc B-dc with a 45 Hz AC field across a range of B-ac between 7.9 and 21 mG(rms). Finally, we changed the AC frequency to 25 Hz, with a corr esponding change in B-dc to 203 mG (to tune for the same set of ions a s in the first test) and a B-ac range from 78 to 181 mG(rms). In all c ases the observed responses were consistent with predictions of the IP R model. These experimental results are the first to support in detail the validity of the fundamental relationships embodied in the IPR mod el. (C) 1994 Wiley-Liss, Inc.