Figure 1.

Schematic of the computational model. (A) Electric circuit representation of coupled myocytes. Intracellular nodes are coupled via a myoplasmic resistance (R_myo). End nodes are coupled via a gap junctional resistance (R_gap). Extracellular potentials at the disc and intercellular cleft (${\varphi }_e^{disc}$ and ${\varphi }_e^{cleft}$, respectively) are governed by a T-shaped network of two axial resistances in the intercellular cleft (R_cl) and one radial resistance (R_radial). (B) Na⁺concentration in diffusively coupled compartments, including intracellular Na⁺in the axial and disc compartments (${\left[N{a}^{+}\right]}_i^{ax}$ and ${\left[N{a}^{+}\right]}_i^{disc}$) and extracellular Na⁺in the intercellular cleft and bulk spaces (${\left[N{a}^{+}\right]}_e^{cleft}$ and ${\left[N{a}^{+}\right]}_e^{bulk}$). (C) Representation of age-associated change in model parameters, including changes in cell size (S), Na⁺ channel density (ρ_Na), and Na⁺channel ID localization (ID_Na).