FIG. 8.

The period generally increases as the cleft volume $vcl$ increases for various combinations of fractions $f_{K1}$ for cell 1 and 2 ( $f_{K1}^{(1)}$, $f_{K1}^{(2)}$). Curves that abruptly end, which have less than five dots (e.g., top maroon curve $(0.925,0.85)$), indicate that automaticity is extinguished for larger $vcl$. We considered five total values of $vcl$. Note that we only show the case of no gap junction coupling ( $g_{gap}=0$), as differences in period duration for $g_{gap}>0$ values are negligible. Only cell-1’s period is shown, because in all cases, the period duration differences between cells 1 and 2 are less than a fraction of a millisecond.