FIG. 6.

Ephaptic impulse transmission. Panel (a): Electrical equivalent circuit of two cells (green) and the cell-to-cell junction in between. Each cell contains two excitable membrane elements (black, Luo-Rudy system of ion channels in parallel with membrane capacitance), connected by cytoplasmic resistors. The cell junction is modeled by (1) resistors representing gap junction channels formed by connexins (blue), (2) an excitable element representing ion channels located in the intercalated disk cell membrane (red), (3) a pair of cleft resistors, and (4) a radial resistor connecting the cleft to the extracellular space. This space is set to zero reference potential. Panel (b): Dependence of propagation velocity in a strand composed of cells modeled in panel (a). Propagation velocity is plotted against cleft width for a bundle of curves representing a decreasing degree (from top to bottom) of resistive coupling by gap junction channels. A biphasic behavior of propagation is observed for reduced resistive coupling < 30%. For very low degrees of coupling, propagation is preserved if cleft width is < 40 nm. Reproduced with permission from J. P. Kucera et al., Circ. Res. 91, 12 (2002). Copyright 2002 Wolters Kluwer Health, Inc.⁴⁶