Figure 4.

I_NaP magnitude is larger than I_M at perithreshold potentials. Voltage clamp experiments were designed to measure I_NaP and I_M consecutively in the same CA1 neurons. (A) A voltage ramp protocol was used to isolate I_NaP by a subtraction method. The slow depolarizing ramp (46.6 mV/s) inactivates transient Na⁺ current in control condition (black) but allows the induction of the persistent current. After addition of 1 μM TTX I_NaP is blocked (red). Isolated I_NaP trace is obtained by subtraction of these two recordings (green trace). (B) Representative whole-cell I_NaP vs. command potential curve. (C) Average G_NaP vs. command potential curve calculated from whole-cell currents curves divided by the driving force (V_m-E_Na, n = 13). (D,E) Protocol used to measure I_M. Neurons were held at −87.5 mV and a family of 2 s depolarizing squared voltage pulses were used to explore potentials between −77.5 and −32.5 with 5 mV steps, at control conditions (D) and after bath addition of 10 μM of XE991 (E). (F) I_M traces are isolated by subtracting recordings in XE991 from those in control condition. (G) Representative whole-cell I_M vs. command potential obtained from (F) (current was measured as the average of the last 50 ms of the pulse response). (H) Average G_M vs. command potential curve (n = 13). Individual conductance curves were obtained dividing I_M by V_m-E_K. (I) Overlap of G_NaP and G_M curves shown in C and H, respectively. Continue G_NaP curve was quantized extracting values at same potentials explored for G_M. (J) Paired comparison of G_NaP and G_M obtained at three near threshold potentials (n = 8). (K) Paired comparison of I_NaP and I_M calculated using reversal potentials from current clamp condition (n = 8). Two-way repeated measures ANOVA, ^***P < 0.001.