WEAK ELECTROMAGNETIC FIELD EFFECTS ON NEUROTRANSMITTERS IN CULTURED NERVE CELLS

Abstract

The electrochemical information (ECI) transfer hypothesis states that bioeffects of weak, pulsed electromagnetically induced current (PEMIC) are mediated by ion/dipole binding and transport at the plasma membrane. Although considerable experimental evidence for the binding and transport of calcium ions in this response has been presented, the possible role of other ions has been largely unexplored, with the possible exception of Na/K ATPase. It was therefore of interest to determine whether PEMIC might alter sodium dependent membrane processes. Carrier mediated membrane co-transport was chosen since it is known to be highly dependent on extracellular sodium(Na_o) and chloride ion concentrations. Facilitated transport of macromolecules(eg.amino acids,sugars and hormones) involves the binding of Na_o and the substrate to independent sites at the extracellular side of the membrane carrier followed by translocation of the carrier.

Norepinephrine(NE) transport into cultured PC12 nerve cells was chosen as a model system since these cells are a well characterized model system with neurochemical properties similar to those in normal nervous tissue. The initial, uptake of (³H)-NE was measured by preincubating PC12 cells with ImM pargyline, an MAO inhibitor which prevents intracellular metabolism of NE.During the lOmin incubation of the cells with (³H)-NE(0.4uCi/ml), the cells were exposed to either control or electromagnetic environments at room temperature. PEMIC stimulation was applied with 10 cm coils using the clinically active repetitive pulse burst signal (200 μsec main polarity, 20 μsec opposite polarity, 5 msec burst, 15Hz overall frequency). dB/dT in the main polarity is 0.1 G/μsec corresponding to an induced electric field of 1 mV/cm. The cells were then washed three times to remove NE non-specifically bound to the plasma membrane. Intracellular NE taken up from the extracellular medium was then counted for radioactivity and expressed relative to total cellular protein.

The results indicate that NE transport is inhibited by 34.5% ± 4.4 in the presence of PEMIC. In order to determine whether PEMIC inhibits uptake by competing with the binding of Na_o to the membrane carrier, Na_o was lowered from 120mM to 9mM during PEMIC exposure. Although lowering Na_o inhibited neurotransmitter uptake by 78.5% ± 1.5, PEMIC had no additional inhibitory effect (84.0% ± 3.9). Although this suggests that sodium and PEMIC may be acting at the same site, other Na concentrations must be examined to verify this conclusion. To determine whether inhibition of transport by PEMIC occurs at the neuro- transmitter binding site,the specific inhibitor,desmethyllmlpramine(DHI), was used to compete with NE binding.In the absence of PEMIC, DMI blocked uptake in a typical concentration dependent manner. At 10^-8M DMI, PEMIC had no additional Inhibitory effect on NE uptake (45 vs 47%). However, at lower DMI concentrations (5×10^-9M),PEMIC caused a 79% enhancement of the efficacy of the inhibitor. The results suggest that PEMIC affects either the Na_o, and/or NE binding site on the external plasma membrane. Experiments with varying Na_o and NE concentrations will determine the specificity of this interaction.

PC12 cells were also used to study the effect of PEMIC on calciumdependent neurotransmitter release. Noradrenaline release was previously shown by the author to behave in a similar manner to normal brain tissue. Cells were placed between two concentric coils connected in parallel to a driving circuit and pulse generator producing a train of adjustable square pulses with a pulse width of 0.6ms giving an overall frequency of 516Hz. The magnitude of the resulting magnetic field varied between 1.6 and 8.5 Gauss with the electric field strength in the medium ranging from +0.038 to -0.019 V/m. (³H)- Noradrenaline release was monitored from cells preloadcd with the radiolabelled neurotransmitter by measuring extracellular noradrenaline to generate a spontaneous efflux curve. Fifteen minute exposure to the electromagnetic field resulted in a 28% increase in noradrenaline release(p<0.001). The effect was blocked in the presence of elevated magnesium suggesting a requirement for extracellular calcium. Subsequent pilot studies suggest that the effect is also dependent on the rise time and frequency of the square pulses in a non-linear fashion.

These results indicate that PEMIC may cause biological effects by modulating the action of sodium and calcium ions in the extracellular space. The resulting increase in noradrenaline release and decrease in noradrenaline uptake observed in these experiments indicates an overall enhancement of the adrenergic nervous system. This novel stimuli may also be able to be used clinically to treat psychiatric disease involving the adrenergic nervous system.