Fig. 3.

Effect of 10 nM VX-548 on action potentials during repetitive firing. (A) Firing evoked by a 1-s 300-pA current injection before and after application of 10 nM VX-548. (B) First 100 ms on an expanded time scale. (C) Phase-plane plot of dV/dt versus V for the first action potential. (D) Collected results for effect of 10 nM VX-548 on peak of the first action potential (Left) and 4th action potential (Right). Peak of first action potential was +54 ± 2 mV in control and +43 ± 4 mV in VX-548 (mean ± SEM, n = 21; P = 0.0001, two-tailed Wilcoxon signed rank test) with an average decrease of 11 ± 2 mV. Peak of 4th action potential was +47 ± 4 mV in control and +20 ± 4 mV in VX-548 (mean ± SEM, n = 11; P = 0.0036, two-tailed Wilcoxon signed rank test) with an average decrease of 28 ± 3 mV. (E) Collected results for effect of 10 nM VX-548 on width of first action potential, measured at half-maximal amplitude. In 16 of 21 cells, the width decreased with VX-548; in the 5 cells where width at half-maximal amplitude increased, peak was greatly reduced so that half-maximal amplitude occurred much more negative than in control. Average widths were 2.92 ± 0.33 ms in control and 2.66 ± 0.48 ms in VX-548 (mean ± SEM, n = 21; P = 0.197, two-tailed Wilcoxon signed rank test).