Properties of sodium and potassium channels of the squid giant axon far below 0°C

Summary

Squid giant axon could be excited in concentrated glycerol solutions containing normal concentrations of electrolytes, when osmolalities of solutions inside and outside the axon were matched. These glycerol solutions did not freeze at the temperature as low as −19°C. The nerve excitation in these solutions were observed at this low temperature. The excitation process at this low temperature was slowed down and time constants of the excitation kinetics were several hundredfold larger than those in normal seawater at 10°C, under which temperature the squid habituated. The temperature coefficients for the electrophysiological membrane parameters under this condition were larger than those in normal seawater above 0°C. The Q₁₀ value for the conduction velocity was 2.0 and that of the duration of the action potential was around 8.5. The time course of the membrane currents was also slowed with the Q₁₀ value of around 5 and the magnitude decreased with the Q₁₀ value of around 2 as the temperature was lowered. The Q₁₀ values for the kinetics of the on process of the Na-channel were around 4.5 and were almost the same as those of the off process of the Na-channel in the wide range of the temperature below 0°C. The Q₁₀ value of the on process of K-channel was around 6.5 and was larger than those for Na-channel. The Q₁₀ values increased gradually as the temperature was lowered.