Effect of Low Sodium, Tetrodotoxin, and Temperature Variation upon Excitation

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Abstract
[long dash]The lowering of external Na raised both the constant quantity threshold, Qo, and the rheobase, Io, in both real space-clamped squid axons and the theoretical axon as computed on the basis of the standard Hodgkin-Huxley equations. In both real and theoretical axons the minimum intensity for excitability for short pulses, which occurs at about 15[degree]C, was still present when low Na replaced seawater. Low Na did not affect the temperature dependence of the strength-duration relationship in the range, 5[degree] to 25[degree]C. The excitability of tetrodotoxin-treated real axons was found to be more temperature-dependent than that of normal real axons. Also the data on dosage-response to TTX of real axons fit the dose response relationship of a hypothetical system in which one TTX ion binds reversibly to its receptor to produce a fraction of the inhibitory effect, the curve being identical to a simple adsorption isotherm. The Hodgkin -Huxley equations describe the broad outline of events occurring during excitation quite well.