Model investigations of the temperature dependence of demyelinated and reorganized axonal membrane

Abstract

The temperature dependence (from 10 degrees to 50 degrees C) of the intracellular action potentials' parameters in a fiber with a simulated reorganization of the axonal membrane against the background of a systematic paranodal demyelination of the fiber was investigated. The temporal and spatial distribution of the potential as well as the ionic currents' kinetics have been represented. The reorganization of the axonal membrane was achieved by means of potassium channels blocking and increase of the sodium-channel permeability, while the demyelination was achieved by means of elongation of the nodes of Ranvier. In order to account for the temperature dependence of the rate constants and of the maximal sodium and potassium permeabilities, the temperature coefficients (Q10) have been used. It has been shown for the demyelinated and reorganized membrane that increased temperature blocks the conduction at temperatures much higher than the blocking temperature for the demyelinated fiber only. When temperature increases the amplitude of the potential decreases while the velocity increases up to temperatures approaching the blocking temperature after which it abruptly drops. The dependence of the asymmetry and the wavelength of the potential on temperature is complex and nonmonotonic. For the reorganized membrane at the background of a given degree of demyelination with increasing temperature the ionic currents' flow and the membrane conduction respectively increase, but, at lower temperatures, when the temperature increase is combined with the increased degree of the fiber demyelination, the conduction is blocked.