Fig. 2. Reduction of I_Na amplitude without change in activation or fast-inactivation.

A: The middle and lower family of traces plot the I_Na recorded 2–3 min before and 14–17 min after beginning of application of 14 µM SKF-38393, respectively. The upper family of traces plots the membrane potential recorded during these currents. The holding potential was −72 mV. Test potentials were incremented from −67 to +3 mV, in 5-mV steps. Recordings were made with K⁺-free external and electrode solutions. Each voltage command was run twice in this cell, and every trace shown is the average of the data pairs recorded. Leak and capacitive currents were subtracted off-line. B–E: current measurements before (black) and after (red) SKF-38393 application, plotted against test potential. B: amplitude of current peaks in A. The lines are the best fits to third order Boltzmann functions multiplied by the Goldman-Hodgkin-Katz (GHK) current equation. C: Activation curve (I_Na amplitude after correction for the instantaneous current rectification calculated by the GHK current equation). The lines are the best fits to third order Boltzmann functions. D: Time from onset of test depolarization to I_Na peak. Lines, single exponential fits. E: Time for I_Na to decline from peak to half-peak amplitude. Lines, single exponential fits. C–E plot mean ± 1 S.E.M. of data from 5 cells.