Figure 1. DHPG or glutamate inhibits fast inactivating Na⁺ current in neocortical pyramidal neurons.

Aa, the normalized value of peak inward Na⁺ current evoked by a voltage step from −70 to −20 mV in an acutely dissociated neocortical neuron (see inset) is plotted as a function of time. b, bath application of DHPG (150 μm) induced a 25% reduction of the amplitude that partially recovered after washout (c). B, plot of average (mean ± s.e.m.) normalized peak current evoked by a step from a holding potential of −70 mV to −20 mV as a function of time. DHPG induced a stable depression of the Na⁺ current (○). Peak amplitude was stable in control experiments (•). C, inhibition of the Na⁺ current induced by glutamate. Top, representative Na⁺ currents evoked by a step from −70 to −20 mV. Bottom, time course of the inhibition. D, in L5 pyramidal neurons (inset), DHPG induced a 20% reduction in the peak Na⁺ current amplitude evoked by a voltage step from −70 to −20 mV. External Na⁺ concentration: 125 mm.