Action of 50 Hz magnetic fields on neurite outgrowth in pheochromocytoma cells

This study tests the capacity of 50 Hz magnetic and electric fields to stimulate neurite outgrowth in PC-12D cells, a cell line which originated from a pheochromocytoma in rat adrenal medulla. The cells were plated on collagen-coated, plastic petri dishes and exposed to sinusoidal 50 Hz magnetic fields for 22 h in a 5% CO2 incubator at 37 degrees C. Two 1,000 turn coils, 20 cm in diameter, were assembled in a Helmholtz configuration to generate a magnetic field in a vertical orientation, thereby inducing a companion electric field in the dish with intensity proportional to radius. A magnetic-field shield housed the control samples in the same incubator. Total cells and number of cells with neurites at least as long as one cell diameter or having a growth cone were counted within a radius of 0.3 cm of the dish center and within an annulus of 1.7-1.8 cm radii in 60 mm dishes, at 3.6 cm radius in 100 mm dishes, and between 1.9 and 2.1 cm radii in the outer well of organ cultured dishes, which are physically separated into two concentric wells. Sham exposure demonstrated no difference in percentage of cells with neurites between the exposed and control locations in the incubator. Exposures were done at 4.0, 8.9, 22, 29, 40, 120, 236, and 400 milliGauss (mG). At dish radii of 1.7-1.8 cm in the 60 mm dishes these magnetic flux densities induced electric fields of 1.1, 2.5, 5.9, 8.1, 11, 33, 65, and 110 microV/m, respectively, while within a radius of 0.3 cm, the induced electric fields were less than 0.2, 0.4, 1.0, 1.5, 1.9, 6.0, 11, and 19 microV/m, respectively. For other dishes, the larger radii produced proportionally larger induced electric fields. At each field strength, there were two control dishes and four to nine exposed dishes; 100 or more cells were counted at each location on the dishes. The results demonstrate that magnetic fields stimulate neurite outgrowth in a flux-density-dependent manner between 22 and 40 mG, reaching an apparent stimulation plateau between 40 and 400 mG; no effects were seen at 8.9 mG or lower. There was no apparent neurite stimulation due to the electric field. Although relatively low intensity (> or = 22 mG) magnetic fields alone can stimulate a morphological response in a cell which is normally stimulated by nerve growth factor molecules binding to membrane receptors, the chemical basis of this response is unknown.