Effect of temperature on the potential and current thresholds of axon membrane.

The effect of temperature on the potential and current thresholds of the squid giant axon membrane was measured with gross external electrodes. A central segment of the axon, 0.8 mm long and in sea water, was isolated by flowing low conductance, isoosmotic sucrose solution on each side; both ends were depolarized in isoosmotic KCl. Measured biphasic square wave currents at five cycles per second were applied between one end of the nerve and the membrane of the central segment. The membrane potential was recorded between the central sea water and the other depolarized end. The recorded potentials are developed only across the membrane impedance. Threshold current values ranged from 3.2 microa at 267deg;C to 1 microa at 7.5 degrees C. Threshold potential values ranged from 50 mv at 26 degrees C to 6 mv at 7.5 degrees C. The mean Q(10) of threshold current was 2.3 (SD = 0.2), while the Q(10) for threshold potentials was 2.0 (SD = 0.1).