Weak sinusoidal electric fields modify the calcium efflux from freshly isolated chick and cat cerebral tissues bathed in Ringer's solution, at 360. Following incubation (30 min) with radioactive calcium (45Ca2+), each sample, immersed in fresh solution, was exposed for 20 min to fields at 1, 6, 16, 32, or We have previously described a sharply increased efflux of calcium from isolated chick brain tissues exposed to modulated radio frequency fields (16). These studies showed that the response depended on a narrow band of slow modulation frequencies (6-25 Hz), and not on the presence of the unmodulated carrier wave alone (147 MHz, 0.8 mW/cm2). In the present study, chick cerebral hemisphere and cat cerebral cortex were exposed, in vitro, to weak (5-100 V/m) extremely low frequency (ELF) fields (1-75 Hz).
MATERIALS AND METHODSField exposure was performed in an environmental screened chamber, between two parallel metal plates, one square meter in area, 50 cm apart. Sine wave electric fields were applied to the plates at levels of 5-100 V/m and at frequencies of 1-75 Hz. Equal voltages with respect to ground were applied to each plate.Chick cerebral hemispheres were rapidly removed following decapitation. The hemispheres were separated and after weighing each was incubated at 36' for 30 min in 1 ml of a physiological medium [155 mM NaCl, 5.6 mM KCI, 2.16 mM CaCl2, 24 mM NaHCO3, and D-glucose (2 g/liter)] together with 0.2 ml of a solution containing 45Ca2+ (0.2 1ACi, specific activity 1.39 Ci/mmol). The incubated samples were then rinsed three times and exposed for 20 min to an environmental electric field while immersed in 1.0 ml of the physiological medium. At the conclusion of field exposure, an aliquot of 0.2 ml of the bathing solution was taken for scintillation counting. Prior to counting this aliquot was mixed with 9.0 ml of a scintillation adjuvant (Packard Dimilume). The brain samples were dissolved overnight in a digestive medium (Soluene 350, Packard) and then assayed for radioactivity. For each field condition (in both frequency and amplitude) "sets" of 10 brain samples were used simultaneously in field exposure and control conditions. Control samples were tested identically to the test samples except for the field exposure. All tissues were maintained at 36' during the whole experiment (16).The same experimental procedure was applied to striated muscles (lateral head of the gastrocnemius) in a series of chicks to evaluate possible effects in nonnervous tissue. Fifty muscle specimens were tested with 20 V/mi, 16 Hz field and compared with nonexposed muscles (30 samples). The statistical treatment of the data was identical to that applied to brain tissues.Samples of freshly removed cat cortex were similarly tested. Under ether anesthesia, the cerebral hemispheres were exposed. After completion of surgery, general anesthesia was discontinued and local anesthesia was instituted in all incisions and pressure points and thereafter the animal was immobilized with gallamine triethiodide (6.0 mg, intra...
