TEMPERATURE EXPERIMENTS ON NERVE AND MUSCLE MEMBRANES OF FROGS - INDICATIONS FOR A PHASE-TRANSITION

The influence of temperature changes in the range of 25°C to -6°C on the time constants of Na activation (τm) and inactivation (τh) was studied in twitch muscle fibers and the node of Ranvier under voltage-clamp conditions. Arrhenius plots of τm and τh exhibit a change in activation enthalpy at temperatures below 10°C. Cooling and subsequent heating induce a hystersis in the temperature dependence of τm and τh Ni2+ and UO22+ increase the hysteresis width. With fast temperature changes the gating kinetics relax to their new values more slowly than the temperature change. Hence, temperature must be changed more slowly than 5°C/min if an additional apparent hysteresis due simply to this relaxation is to be avoided. The data are explained by the hypothesis of a phase transition in the membrane lipids. This conception is favoured over a temperature-induced change in protein conformation, since the neutral local anaesthetic benzocaine shows use-dependent block as if low temperature restricted the access of the drug through the lipid phase to its receptor. © 1979 Springer-Verlag.