Extended Data Fig. 5: Elementary mechanisms underlying FHF1A regulation of INa,L.
a, FL distributions for NaV1.5 IFM/IQM at baseline (black line and gray shaded area; n = 231 sweeps from 3 one-channel recordings) and upon overexpression of FHF1A (red line and rose shaded area; n = 217 sweeps from 5 one-channel recordings). FL denotes the probability that the first opening occurred at time < t. FHF1A had minimal effect on the FL distribution for the IFM/IQM mutant. b, FL distributions for NaV1.5 LILA/WICW at baseline (gray shaded area; n = 176 sweeps from 3 one-channel recordings) and under overexpression of FHF1A (rose shaded area; n = 270 sweeps from 6 one-channel recordings). FHF1A decreased the pedestal value of FL for the LILA/WICW mutant suggesting that FHF1A increases closed-state inactivation. p < 0.001 by KS-test. c, Open-duration (OD) distribution for NaV1.5 IFM/IQM tallies the durations of a single sojourn to the open state. FHF1A shortens the OD distribution for the IFM/IQM mutant, hinting at potential increase in the rate constant for inactivation from the open state. For IFM/IQM, n = 7597 openings from 6 cells. For IFM/IQM + FHF1A, n = 1332 openings from 9 cells. p < 0.001 by KS-test. d, FHF1A has no effect on OD distribution of the LILA/WICW mutant. For LILA/WICW, n = 22272 openings from 8 cells. For LILA/WICW + FHF1A, n = 1361 openings from 6 cells. e, Conditional open-duration (OD) distribution for NaV1.5 ΔKPQ mutants, for single-level channel openings in the late phase, after 50 ms depolarization, (n = 12278 openings from 12 cells). FHF1A shortened the OD distribution (n = 5011 openings from 12 cells), while FHF1B evoked a minor increase in OD distribution (n = 2269 openings from 6 cells). f-k, conditional OD distributions confirms variable shortening of the OD distribution in the presence of FHF1A for E[1784]K (panel f; control, n = 9355 openings from 15 cells; +FHF1A, n = 1683 openings from 14 cells), S[1904]L (panel g; control, n = 7097 openings from 10 cells; +FHF1A, n = 10 cells and 1929 openings), Q[1909]R (panel h; control, n = 4406 openings from 13 cells; +FHF1A, n = 1658 openings from 11 cells), IQ/AA (panel i; control, n = 5345 openings from 13 cells; +FHF1A, n = 1266 openings from 13 cells; +FHF1B, n = 16360 openings from 13 cells), and Δ1810 (panel j; control, n = 1049 openings from 10 cells; +FHF1A, n = 576 openings from 9 cells), all consistent with the presence of open-state block. The Δ1885 mutant failed to show any appreciable change in OD distribution (panel k; control, n = 3955 openings from 10 cells; +FHF1A, n = 2195 openings from 9 cells). As FHF1A inhibits INa,L for this mutant, this effect likely modifies the closed state. l, Bar graph summary of mean OD calculated from OD distribution function in panels. e-k from sample sizes noted in each panel. Each bar, mean OD value. e-k, Statistical Analysis, p < 0.001 for comparisons of OD distribution absent FHF to with FHF1A for ΔKPQ, E[1784]K, S[1904]L, Q[1909]R, IQ/AA, and Δ1810 mutants by KS-test.
