Uptake of local anaesthetics: movement of ethanol into frog sciatic nerve

The changes of nerve action potential with time of the excised bullfrog sciaticperoneal nerve were measured at 24 degrees C with the nerve immersed in oxygenated mineral oil containing various concentrations of ethanol. One series of measurements was made with intact nerve and a range of about 20 to 110 millimolar ethanol. Another series was made with nerves in which the epineural sheath was cut open longitudinally and using a range of about 15 to 51 millimolar ethanol. The results were analysed by means of simple diffusion theory, and below applied ethanol concentrations of about 70 millimolar the latent periods and times to total block fitted the theoretical pattern well. Disagreements between theory and measurement of previous workers is explainable by their neglecting to recognize that nerve bundles do not extend to the nerve periphery. It was found that the minimum oil concentration of ethanol capable of producing total block is 15 millimolar. Above 70 millimolar, behaviour was observed consistent with nerve damage. It was found possible, by measuring the ratio latent period: time to total block, to separate the relative contribution of the epineural sheath and epineurium as a diffusion barrier to ethanol from that of the perineurium and perilemma.