Persistent Na⁺ currents recorded from NG2 cells in hippocampal slices. (A) Superimposed membrane potential changes in an NG2 cell and a pyramidal neuron in response to a series of current injections (300 ms in duration with an interval of 15 s) from a holding potential of −70 and −60 mV, respectively. In the NG2 cell, only a single small spikelike depolarizing transient (arrow) could be evoked upon each super-threshold depolarizing current injection. (B) Comparison of the kinetics of Na⁺ currents recorded from a NG2 cell with those recorded from a neuron evoked by a depolarizing voltage pulse at −20 mV. (C) Example recordings from NG2 cells showing phenytoin-induced persistent outward current at −41 or −31 mV holding membrane potential and its blockage by intracellular loading QX314 (5 mM; bottom trace). (D) Mean amplitude of phenytoin-induced outward currents recorded at various membrane potentials as shown in C. The number associated with each column refers to the number of cells examined in each condition. *, P < 0.05 compared with the group as indicated. (E) Perfusion with riluzole also revealed an apparent persistent outward current at depolarizing membrane potentials. (F) Mean amplitude of riluzole-induced outward currents recorded at various membrane potentials as shown in E. Error bars represent mean ± SEM.