Nerve impulse blockage in squid axons by n-alkanes: the effect of axon diameter

1. The anaesthetic effects of aqueous solutions of the n-alkanes pentane to nonane on the propagated action potential of squid axons have been investigated for a range of axon diameters. 2. By the use of small axons (approx. 200 microns diameter) to minimize effects due to long diffusion times and alkane depletion it was found that n-pentane and n-hexane caused a rapid reversible inhibition of the impulse, while higher homologues had progressively less effect, n-nonane being apparently inert. 3. The rate of action potential decline due to the n-alkanes was found to be strongly dependent on axon diameter. For n-hexane, n-heptane and n-octane the rate of decline was inversely proportional to the square of the axon diameter. 4. The mechanisms which may underly the increased sensitivity of small axons to impulse blockade by n-alkanes are discussed. A quantitative comparison is made between the effects of n-hexane, n-heptane and n-octane on the action potential. It is argued that this supports the idea of a real decline in anaesthetic potency on ascending the homologous series, rather than an effect due to long diffusion times and solution depletion.