Intracellular recording during magnetic field application to monitor neurotransmitter release events: methods and preliminary results.

Abstract

A method for simultaneous magnetic field application and intracellular recording is presented. A little used method for magnetic field application was exploited; the field generator consisted of a flat copper sheet through which current was passed to generate a magnetic field. The resultant magnetic field was relatively homogeneous, exhibiting a variation of +/- 5%. This compact, current-sheet field generator was mounted on the condensor of a microscope. The current induced in the intracellular electrode was reduced by injecting current equal and opposite to the induced current into the microelectrode. This step reduces the possibility of cellular effects and voltage artifacts due to the induced electrode current. The technique was used to conduct preliminary studies on the effects of extremely low frequency (ELF) linearly and circularly polarized magnetic fields (1.0 Gauss, 60 and 70 Hz) on miniature end plate potential (mepp) frequency (frequency of neurotransmitter release events) of rat flexor digitorum brevis muscle. The same synapse was utilized for both the sham-exposed control and the exposed experimental halves of an experiment. After 10 min of exposure to a 60-Hz linear field, mepp frequency was significantly increased by 12%, but exposure to a 60-Hz circular field did not significantly alter mepp frequency. Exposure to a 70-Hz linear field did not significantly change mepp frequency, but application of a 70-Hz circular field appears to decrease mepp frequency by 4%. These results indicate that both types of magnetic fields can alter mepp frequency, depending upon the frequency and configuration of the field.