Propagation of APs simulated by PSpice through the 10 × 10 network of 100 cardiac muscle cells. There were zero transverse gj-channels (Rgj = 100,000 MΩ). The termination resistance at the ends of the chain (Rbt) was 1.0 KΩ, similar to that for the fluid bathing the surface of the network. The 4 panels show the effect of varying the number of longitudinal gj-channels in each chain from zero (panel A, Rgj = 100,000 MΩ) to 10 (panel B, Rgj = 1,000 MΩ), 100 (panel C, Rgj = 100 MΩ) and 1,000 (panel D, Rgj = 10 MΩ). Note the presence of a hyperpolarizing after-potential following the repolarizing phase of the AP. When there were many gj-channels (C, D), the APs of all 10 cells in each chain were superimposed, indicating extremely fast longitudinal propagation within each chain. Therefore, only 10 traces are evident, one for each chain. Note that the TPT was slightly lengthened for 100 and 1,000 gj-channels compared to 10 channels (i.e., a higher degree of cell coupling actually inhibited the overall propagation velocity).