Squid Giant Axon: Repetitive Responses to Alternating Current Stimulation

Abstract

SINUSOIDAL alternating currents were used by Hill, Katz, and Solandt¹ to stimulate the frog sciatic nerve. At low frequencies of stimulation, repetitive responses caused discrepancies between the observed threshold values of current and the values predicted by Hill's theory of excitation². Teorell³ used triangular-wave alternating currents to excite action potentials in the Nitella cell. At low stimulus frequencies, two spikes per current cycle were occasionally observed. Repetitive all-or-none responses to constant currents were reported by Katz⁴ in frog sciatic nerve, by Hodgkin⁵ in single crustacean axons, and by Hagiwara and Oomura⁶ in the squid giant axon. Hagiwara and Oomura⁶ also stimulated the squid giant axon with linearly rising currents. In these experiments, single-action potentials were followed by a steadily increasing depolarization of the membrane, but repetitive action potentials did not occur. Tasaki⁷ obtained similar results when he used linearly rising currents to excite single toad-nerve fibres. The present research was undertaken to determine whether the squid giant axon could produce repetitive all-or-none responses to triangular-wave and sinusoidal alternating-current stimuli and to observe the responses at various current amplitudes and frequencies.