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Action Potentials Occur Spontaneously in Squid Giant Axons with Moderately Alkaline Intracellular pH

¹ Laboratory of Neurophysiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
² Department of Physiology, McGill University, Montreal, Quebec, Canada, H3G1Y6

* To whom correspondence should be addressed. E-mail: jrclay{at}ninds.nih.gov

This report demonstrates a novel finding from the classic giant axon preparation of the squid. Namely, the axon can be made to fire autonomously (spontaneously occurring action potentials) when the intracellular pH (pH_i) was increased to about 7.7, or higher. (Physiological pH_i is 7.3.) The frequency of firing was 33 Hz (T = 5°). No changes in frequency or in the voltage waveform itself were observed when pH_i was increased from 7.7 up to 8.5. In other words, the effect has a threshold at a pH_i of about 7.7. A mathematical model that is sufficient to mimic these results is provided using a modified version of the Clay (1998) description of the axonal ionic currents.

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