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Figure 2. SI onset and recovery for L689I channels: Ionic and gating currents. SI induction and recovery of ionic and gating currents measured as described in our companion paper (Silva and Goldstein, 2013). Groups of four to seven cells reported as mean ± SEM. (A) SI is probed by 320 repetitions of a triple-pulse protocol from a holding potential of −100 mV: a 5-ms test pulse to +45 mV was used to measure peak current (phase a); SI was induced by a 500-ms pulse at −100, −75, −45, −15, 15, or 45 mV (phase b); and a 30-ms pulse at −100 mV used (phase c) to allow for recovery from fast inactivation before the next test pulse. Above the protocol, sample traces are shown for cycles 1, 2, 80, and 320 and demonstrate progressive decrease in peak current with SI at +45 mV. Dotted-dashed lines correspond to data reported previously with WT (Silva and Goldstein, 2013). Parameters for L689I SI onset are reported in Table 1. Insets compare L689I ionic current (circles) at 160 s to WT (triangles). (B) Loss of gating current with SI induced as in A. (Top) Sample traces from cycles 1, 2, 80, and 320 show progressive reduction in peak gating current with SI at +45 mV. (Bottom) Plot of the gating charge (Q, the integral of the gating current) with time at different potentials. Insets compare L689I gating current at 160 s to WT. (C) Sodium current. (Top) Recovery from SI is probed after induction pulses to +45 mV for 5, 40, or 160 s (phase a) during 5,000 cycles of 20 ms at −100 mV (phase b), followed by 4 ms at +45 mV when peak current is recorded (phase c). Sample traces from cycles 1, 2, 500, and 5,000 show the recovery of peak current. (Bottom) Voltage and cycle dependence of recovery from SI on log–log plots of peak current. Parameters for recovery from SI are shown in Table 2. Dotted-dashed lines correspond to data reported previously with WT (Silva and Goldstein, 2013). (D) Gating current. Recovery from SI is probed as in A, with 2 µM TTX. Image published in: Silva JR and Goldstein SA (2013) © 2013 Silva and Goldstein. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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