Loosening of paranodal myelin by repetitive propagation of action potentials

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Abstract
We have previously shown by X-ray diffraction techniques that the stability of the myelin lattice is decreased by repetitive stimulation of the nerve1. We now show that in rat myelinated fibres this structural change is accompanied by the appearance of voltage-sensitive potassium channels which do not normally participate in the generation of the action potential. Since it has previously been shown that structures associated with potassium channels are found in the internodal and paranodal axolemma membrane but are normally concealed under the myelin sheath2,3, we suggest that the acceleration of myelin swelling after repetitive propagation of the action potential may be due to the opening of paranodal axoglial junctions. To our knowledge this is the first demonstration that nerve activity may regulate the structural properties of the paranode.