Fast inactivation properties of sodium channel currents in lamina I/II neurons. Voltage protocols are shown throughout for corresponding recording traces. For visual clarity, only a selected time period from a subset of recording sweeps are shown. A) Onset of closed-state inactivation. Left, representative sodium channel current traces following conditioning steps of variable length to -70 mV. Scale bar x axis = 50 ms, y axis = 100 pA. Right, fraction of sodium channel current that becomes inactivated for a given sweep normalized to peak current in the first sweep (n = 9). Vhold = -100 mV. B) Recovery from fast inactivation. Left, representative sodium channel current traces. Scale bar x axis = 50 ms, y axis = 100 pA. Right, average fraction of P2 sodium channel current relative to P1 current amplitude (n = 10). Vhold = -100 mV. C) Sodium channel currents elicited during ramp depolarizations (right; Vhold = -100 mV) are only a small fraction of the amplitude of peak currents produced during a standard IV protocol with depolarizations between -60 mV and -20 mV (left). Scale bars x axes = 5 ms, y axes = 100 pA. LJP = 4.2 mV, uncorrected.