Gating pore currents in HypoPP mutant channels. (A) The gating pore current was measured as the steady-state current at the end of a 150-ms pulse that was leak corrected by subtraction of the average steady-state current recorded from oocytes expressing WT Na_V1.4. The gating pore current from each oocyte was normalized by Q_{on_max} for the same egg and plotted as a function of test potential. Symbols show mean and SEM for R669H mutants (blue; n = 32) and for R672G mutants (red; n = 18). Error bars represent ± SEM. (B) The correlation between the gating pore current measured at −140 mV and Q_{on_max} is shown as a scatter plot. Each symbol represents the response from a separate oocyte. Lines show the best fit constrained through the origin. The correlation for I_GP–Q_{on_max} had much less variance than for I_Na–Q_{on_max} measured from the same set of oocytes (Fig. 3 A).