Fig. 7.

Resolved regions of two different three-dimensional generalizations of our multiscale model. Resistors that cross the boundary of the resolved regions couple the microscale model to the macroscale model at a coarse-fine interface. A presents a detailed model. Shaded regions represent myocytes connected to their neighbors through gap junctions on their sides (depicted as resistors) and ends (not depicted). Cells may also interact at their ends through an ephaptic mechanism similar to that in Fig. 1. Electric potential satisfies the Laplace equation, and resolved cells are coupled to unresolved cells by assuming the potential of intracellular space is continuous and current flux is conserved. B presents a reduced model. The thick lines represent one-dimensional cables that model the shaded cells. In this reduced model, electric potential satisfies equations similar to Eqs. 1–7. Resolved cells are coupled to unresolved cells through discretized cytosolic and gap-junctional resistances that intersect the coarse-fine interface.