Action potential (AP) traces recorded intracellularly in cells 1, 5, and 10 of each of the 20 parallel chains of the cardiac bundle. The order of firing for panel A (cells 5 and 10 of each chain) is given by the inset table at the lower right of the figure. A Zero gj-channels. The first visible trace consists of the superimposition of the 20 AP traces recorded from cell #1 of all 20 chains. B: 100 gj-channels. Each of the three traces visible (cells # 1, 5 and 10, respectively) consists of the superimposition of the 20 APs of the 20 parallel chains.