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Seasonal Variation in Conduction Velocity of Action Potentials in Squid Giant Axons

Joshua J. C. Rosenthal and Francisco Bezanilla
Biological Bulletin
Vol. 199, No. 2 (Oct., 2000), pp. 135-143
DOI: 10.2307/1542873
Stable URL: http://www.jstor.org/stable/1542873
Page Count: 9
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Seasonal Variation in Conduction Velocity of Action Potentials in Squid Giant Axons
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Abstract

To determine whether the electrical properties of the squid giant axon are seasonally acclimated, action potentials, recorded at different temperatures, were compared between giant axons isolated from Loligo pealei caught in May, from relatively cold waters (∼10°-12°C), and in August, from relatively warm waters (∼20°C). Parameters relating to the duration of the action potential (e.g., maximum rate of rise, maximum rate of fall, and duration at half-peak) did not change seasonally. The relationship between conduction velocity and temperature remained constant between seasons as well, in spite of the fact that May axons were significantly larger than August axons. When normalized to the fiber diameter, mean May conduction velocities were 83% of the August values at all temperatures tested, and analysis of the rise time of the action potential foot suggested that a change in the axoplasmic resistivity was responsible for this difference. Direct measurements of axoplasmic resistance further supported this hypothesis. Thus seasonal changes in the giant axon's size and resistivity are not consistent with compensatory thermal acclimation, but instead serve to maintain a constant relationship between conduction velocity and temperature.

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