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.