Panel A shows representative sodium current traces with an inset voltage protocol on top, comparing NaV1.2 IQM alone and with FGF14A, FGF13A, FGF12A, and FGF11A, with scale bars for current and time. Panel B shows conductance–voltage curves with y-axis normalized conductance and x-axis command potential in millivolts, including data points and fitted curves for IQM and each FGF-A isoform. Panel C shows scatter plot of half activation voltage values with y-axis Vh in millivolts and x-axis conditions, including individual data points, mean, and error bars. Panel D shows scatter plot of slope factor values with y-axis z value and x-axis conditions, including individual data points, mean, and error bars. Panel E shows plots of inactivation time constants with y-axis time constant in milliseconds and x-axis command potential in millivolts, including curves and data points for different conditions. Panel F shows current traces at zero millivolts comparing wild type, NaV1.2 with FGF-A, and IQM with FGF-A, with scale bars for current and time. Panel G shows scatter plot of inactivation time constants at zero millivolts with y-axis time constant in milliseconds and x-axis conditions, including individual data points, mean, and error bars.
FGF-A homologues directly produce fast inactivation of inactivation-removed Na V 1.2 channels. (A) Example NaV currents arising from NaV1.2_IQM channels transiently expressed alone (IQM) or coexpressed with the indicated FGF-A subunits (FGF14A, FGF13A, FGF12A, and FGF11A). Currents were evoked by the indicated protocol (top). Colored traces highlight current at −20 mV (blue), 0 mV (red), and +20 mV (green). (B) GV curves for each construct (IQM (black), IQM+FGF14A (red), IQM+FGF13A (blue), IQM+FGF12A (magenta), and IQM+FGF11A (green) are shown with peak current evoked by each test pulse normalized to IMAX. Dashed lines are Boltzmann fits to data points (mean ± SD). (C and D) Graphs of Vh (C) and z (D) from GV curves for each construct along with values for individual cells. Data are expressed as mean ± SD with statistics given in Table S3. (E and F) Voltage dependence of mean inactivation onset for IQM+FGFA homologues with solid block line for NaV1.2 alone, solid colored line for NaV1.2+FGF-A, and symbols for IQM+FGF-A. Red, FGF14A; blue, FGF13A; magenta, FGF12A; green, FGF11A. (F) Comparisons of inactivation time course following activation at 0 mV with WT NaV1.2 in black, NaV1.2+FGF-A in a colored line, and IQM+FGF-A as symbols with shaded dotted lines. (G) Mean inactivation time constants ± SD at 0 mV for each FGF-A homologue expressed with NaV1.2_IQM, along with values from individual cells.