Biophysical properties of sodium channel currents in lamina I/II neurons. A) Voltage dependence of activation. Representative sodium channel current traces during depolarizing steps ranging between -60 mV and -10 mV at 10 mV increments. B) Average normalized peak current-voltage relationship for sodium channel current recordings as illustrated in A. C) Voltage dependence of fast inactivation. Representative sodium channel current traces elicited by steps to -20 mV preceded by 100 ms conditioning pulses between -90 and -40 mV at 10 mV increments. Vhold = -100 mV. D) Steady-state activation (black; derived from B) and inactivation (grey) curves. E) Exponential fits of inactivation kinetics from sodium channel currents as in A demonstrate a steep voltage dependence of τinact. n = 13 for all averaged data points. LJP = 4.2 mV, uncorrected.