Effects of temperature on simulated electrotonic potentials and their current kinetics of human motor axons at 20°C–42°C

Abstract

To expand our studies on accommodation in human motor nerve axons, the effects of temperature on polarizing nodal and internodal electrotonic potentials and their current kinetics are investigated. The computations use our temperature dependent multi-layered model of the myelinated human motor nerve fiber and the temperature is increased from 20°C to 42°C. The results show that for temperatures from 28°C to 37°C, the polarizing electrotonic potentials almost coincide, as the kinetics of their ionic currents is changed a little. The normal (at 37°C) resting membrane potential is further depolarized or hyperpolarized during hypothermia (≤ 25°C) or hyperthermia (≥ 40°C), respectively and its change is determined by the flow of ionic currents through the internodal axolemma during the polarizing current stimuli. The polarizing electrotonic potentials are more altered during hypothermia and are most altered during hyperthermia. During hyperthermia, the depolarizing nodal and internodal electrotonic potentials are determined by the nodal slow (I Ks ) and internodal fast (I Kf ) and slow (I Ks ) potassium currents. The hyperpolarizing internodal electrotonic potentials are determined by the activation of internodal channels, which are different during hyperthermia at 40°C and 42°C. These potentials are determined by the internodal I Ks current at 40°C and by the internodal inward rectifier (I IR ) and leakage (I Lk ) currents at 42°C. The difference in accommodation to hyperpolarizing currents during focal and uniform hyperthermia at 42°C is discussed. The present results are essential for the interpretation of mechanisms of threshold electrotonus measurements in subjects with symptoms of cooling, warming and fever, which can result from alterations in body temperature.