FIG. 6.

Detailed bifurcation diagrams for heterogeneous cells, with only ephaptic coupling. The transparent curves are lateral segment voltages in cell-1, and opaque curves are for cell-2. Ephaptic coupling can induce cell-2 to trigger APs in regimes for which, without ephaptic coupling, cell-2 would be quiescent. (a) With cell-1’s fraction of $I_{K1}$ current ( $f_{K1}^{(1)}$) at HB, cell-2’s fraction ( $f_{K1}^{(2)}$) can be slightly less than HB for both cells to trigger APs. (b) For $f_{K1}^{(1)}$ values larger than HB (0.9), the $f_{K1}^{(2)}$ range for which both cells emit APs is larger. (c) For even larger $f_{K1}^{(1)}$ (0.95), the dynamics are similar as in (b); however, for very small $f_{K1}^{(2)}$, there is a regime for which cell-1 triggers APs because it is essentially decoupled from cell-2, while cell-2 exhibits sub-threshold oscillations. For other cleft volumes $vcl$, see Fig. 7(d).