Phenytoin Inhibits the Persistent Sodium Current in Neocortical Neurons by Modifying Its Inactivation Properties
Figure 9
Effect of PHT on depolarized plateau recorded in current clamp.
Depolarized plateau induced by the intracellular injection of a brief (40 ms) depolarizing pulse in a representative neuron recorded in current clamp configuration. Long-lasting depolarizations following the action potential were observed in the presence of K+ and Ca2+ channel blockers and are most likely sustained by the INaP flowing after the fast inactivation of the transient Na+ current. The long depolarized plateau observed under control conditions (A) were shortened in the presence of PHT (100 µM) (B). In five neurons, the decay of the depolarizing plateau was fit by bi-exponential functions; the values of the time-constants were comparable to those describing the time-dependent inactivation of INaP and were significantly shortened by PHT. Panel C shows the mean plateau potentials normalized to their maximal value and the bi-exponential fitting obtained averaging the parameters of the fits of the single cells.