Figure 6. More about this image found in Untitled image

Figure 1. Na ⁺ channel biophysical properties, electrical circuit representation, and spatial distributions. (A) The steady-state activation (left) and inactivation (right) curves, as functions of voltage V, are shown for the baseline (blue) and shifted (red) I_Na subpopulations. (B) Electrical circuit representation of the one-dimensional tissue model (see text for circuit element description). (C) Diagrams of the localization of baseline (blue) and shifted (red) Na⁺ channels for the seven Na⁺ channel distributions considered. Note that the distributions in C correspond with f_Na = 2/3. More about this image found in Na ⁺ channel biophysical properties, electrical circuit repres...

Figure 2. Addition of a subpopulation of I _Na with shifted biophysical properties results in earlier AP upstroke and larger I _Na current in a single cell. (A and B) Transmembrane voltage (V; top and middle; magenta) and I_Na (bottom; blue/red, magenta) are shown as functions of time for a single cell with (A) 50:50 and (B) 30:70 distribution of baseline:shifted I_Na subpopulations. The corresponding voltage and I_Na curves are shown for the homogeneous (only baseline I_Na) single cell in black. In A, I_Na scaled by a factor of 1/2 is shown for comparison with I_Na from the baseline/shifted single cell (dashed black line). More about this image found in Addition of a subpopulation of I _Na with shifted biophysical p...

Figure 3. Na ⁺ current with shifted biophysical properties is proportionally larger and contributes more charge than its conductance fraction in single cells. (A and B) The ratio of the shifted I_Na peak-to-baseline I_Na peak (A; black) and the fraction of charge carried by the shifted I_Na subpopulation Q_Na (B; black) are shown as a function of the shifted I_Na conductance fraction (f_Na). (C and D) The shifted I_Na ratio (C; black) and shifted Q_Na ratio (D; black) are shown as a function of the shifted I_Na-to-baseline I_Na conductance fraction ratio (f_Na/(1 − f_Na)). In all panels, the dashed line represents the expected fraction or ratio, based on the proportion of the shifted I_Na conductance. More about this image found in Na ⁺ current with shifted biophysical properties is proportion...

Figure 4. CV depends on Na ⁺ channel distribution, cleft width, and gap junctional coupling. CV is shown as a function of cleft width (w) for (A–(A-G) G) different Na⁺ channel distributions and gap junction conductance g_gap. For polarized distributions, narrow cleft slows conduction for high g_gap and enhanced conduction for low g_gap. The physiological distribution (mix/homogeneous-polarized) exhibits the greatest sensitivity to cleft width. Parameters: f_Na = 0.7. More about this image found in CV depends on Na ⁺ channel distribution, cleft width, and gap ...

Figure 5. CV depends on Na ⁺ channel distribution, gap junctional coupling, and cleft width. CV is shown as a function of gap junction conductance g_gap for (A–G) different Na⁺ channel distributions and cleft width w. CV slows for decreasing g_gap, with sensitivity to cleft width greater for polarized distributions with the shifted and mix I_Na subpopulations. Parameters: f_Na = 0.7. More about this image found in CV depends on Na ⁺ channel distribution, gap junctional coupli...

Figure 6. The physiological (mix/homogeneous-polarized) distribution exhibits enhanced conduction. (A) CV is shown as a function of gap junction conductance g_gap for cleft widths of 10 (left), 20 (middle), and 30 (right) nm and different Na⁺ channel distributions. (B and C) The ratio of CV for different Na⁺ channel distribution combinations is shown. Parameters: f_Na = 0.7. More about this image found in The physiological (mix/homogeneous-polarized) distribution exhibits enhance...

Figure 7. The physiological (mix/homogeneous-polarized) distribution exhibits sensitivity to cleft widths and Na ⁺ channel redistribution. (A–C) Contour maps of the CV are shown for the (A) baseline/polarized, (B) mix/homogeneous-polarized, and (C) shifted/polarized distributions as functions of cleft width w and f_Na, with 1 cm/s spacing. More about this image found in The physiological (mix/homogeneous-polarized) distribution exhibits sensiti...

Figure 8. Enhanced postjunctional I _Na with shifted biophysical properties promotes faster cell–cell transmission and conduction. (A) Top: Activation time for postjunctional, lateral, and prejunctional membranes for each cell for the baseline/polarized (black) and mix/homogeneous-polarized (magenta) distributions. The change in activation time is shown, adjusted to (middle) cell 24 prejunctional membrane and (bottom) cell 25 postjunctional membrane activation times. (B and C) Intracellular potential φ_i (row 1); cleft potential φ_cleft (row 2); prejunctional (solid) and postjunctional (dashed) I_Na (B, green; C, red) and lateral I_Na (B, black; C, blue; row 3); and gap junction current (row 4) are shown as functions of time for (B) baseline/polarized and (C) mix/homogeneous-polarized distributions. Parameters: g_gap = 100 nS, f_Na = 0.7, w = 10 nm. More about this image found in Enhanced postjunctional I _Na with shifted biophysical properti...

Figure 9. Postjunctional I _Na contributes proportionally more charge than the conductance fraction. (A–C) The fraction of Na⁺ charge Q_Na carried by (A) postjunctional, (B) lateral, and (C) prejunctional I_Na is shown as a function of f_Na, for cleft widths of 10 (left), 20 (middle), and 30 (right) nm and different Na⁺ channel distributions (baseline/polarized, black; mix/homogeneous-polarized, magenta). The dashed black line corresponds with the conductance fraction on each membrane (f_Na/2 on post- and prejunctional; 1 − f_Na on the lateral membrane). Parameters: g_gap = 100 nS. More about this image found in Postjunctional I _Na contributes proportionally more charge tha...

Figure 10. Postjunctional I _Na contribution is enhanced for moderate gap junction coupling. (A–C) The fraction of Na⁺ charge Q_Na carried by (A) postjunctional, (B) lateral, and (C) prejunctional I_Na is shown as a function of gap junction conductance g_gap for cleft widths of 10 (left), 20 (middle), and 30 (right) nm and different values of f_Na for the mix/homogeneous-polarized distribution. More about this image found in Postjunctional I _Na contribution is enhanced for moderate gap ...