The effects of moderate-intensity gradient static magnetic fields on nerve conduction.

Whether exposure to static magnetic fields (SMF) for medical applications poses a therapeutic benefit or a health hazard is at the focus of current debate. As a peripheral nerve model for studies of the SMF effects, we have investigated whether exposure of in vitro frog sciatic nerve fibers to moderate-intensity gradient SMF up to 0.7 T modulates membrane excitation and refractory processes. We measured the changes in the amplitudes of the electrically evoked compound action potentials for three groups: a control group without SMF exposure and two exposed groups with continuous inhomogeneous exposure to maximum flux densities (B(max)) of 0.21 and 0.7 T SMF for 6 h. The values of the nerve conduction velocity of C fibers were significantly reduced by B(max) of 0.7 T SMF during the 4- to 6-h exposure period but not by B(max) of 0.21 T SMF during the entire exposure period of 6 h, relative to the unexposed control. From these findings, we speculate that exposure to moderate-intensity gradient SMF may attenuate pain perception because the C fibers are responsible for pain transmission. Although the mechanistic reasons for this decrease have yet to be clarified, SMF could affect the behavior of some types of ion channels associated with C fibers.