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  • Title: [Membrane currents and action potentials of myelinated nerve fibers and their modification by diphenylhydantoin and tocainide].
    Author: Schwarz JR.
    Journal: EEG EMG Z Elektroenzephalogr Elektromyogr Verwandte Geb; 1988 Sep; 19(3):115-22. PubMed ID: 2460310.
    Abstract:
    A comparison of the ionic currents in single myelinated nerve fibres isolated from the sciatic nerve of the rat and the frog was performed. The nodal membrane of rats lacked almost totally potential dependent potassium channels, whereas in the frog large potassium currents were recorded. Therefore, it was concluded that in mammalian nerve fibres repolarization of the action potential is brought about by the unspecific leakage current and the inactivation of the sodium channels. Phenytoin and tocainide reduced the Na current in nerve fibres of both species. This reduction was due to a potential and frequency dependent block of sodium channels. 50 microM phenytoin and 200 microM tocainide shifted the inactivation curve of the sodium system by 25 mV to more hyperpolarizing membrane potentials. In addition, a decrease in the time interval between repetitive depolarizations increased the amount of Na current reduction. This suggested that in the presence of the drugs the equilibrium between resting and inactive sodium channel states was shifted to more inactivation. The results were successfully interpreted in terms of the "modulated receptor hypothesis".
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