Temperature and impulse velocity in giant axon of squid Loligo pealei

Impulse propagation velocity as a function of temperature in the range 5--20degreesC was obtained by external recording from the giant axon of Loligo pealei. The stellar nerve was set into a chamber allowing continuous superfusion, temperature control, and double recording of the impulse. Velocity was calculated from the interval between the spike peaks. The Q10 of velocity was about 1.8. At all temperatures, the velocity increased with time so that only data obtained during the 1st h or 2 could be generally considered to be comparable. Impulse block occurred below --3.4degreesC, in contrast to the giant axon of L. vulgaris, which blocks at about 0degreeC, but at the higher range of temperatures, the velocity in the L. pealei axons was not as well sustained as in those of L. vulgaris. The expected impulse velocity was calculated from Huxley's stability function f(beta) by approximating that function to a fourth-order polynominal and by substituting into it suitable ratios of available Q10 values relating to membrane conductance, ionic current, capacitance, and axoplasmic resistance. The calculation provided an improved fit to published experimental data on L. vulgaris. The difference in slope of the log velocity versus temperature plots, between the presumably warm acclimatized L. vulgaris and the cold-acclimatized L. pealei, was present in both experimental and calculated curves.