The influences of phenytoin on the fundamental electrical properties of simple neural systems.

The effects of phenytoin on some neurophysiological properties of simple neuronal systems are reviewed. From all the available data phenytoin decreases or has no effect on post-tetanic hyperpolarization, which is interpreted as an expression of the electrogenic pump. Although in some neurons the membrane conductance is increased, the resting membrane potential is minimally affected. The effect on the action potential varies with different preparations and with different neurons of the same ganglion. If an effect is present, the overshoot is decreased or the falling phase is prolonged, or both. Post-synaptic potentials are also affected by phenytoin. EPSPs are decreased in size, while the chloride-dependent, GABA-mediated IPSPs of the crayfish stretch receptor are prolonged. No effect was seen on chloride-dependent, ACh-mediated IPSPs in the abdominal ganglion of the Aplysia. Finally, phenytoin arrests endogenous or pharmacologically induced bursting. Most of the described effects are consistent with the antiarrhythmic and antiepileptic properties of the drug.