Figure 2. Atrial AP plateau is potently modulated by I_NCX.

A) A phase-3 EAD is recorded immediately after (first beat after pause) spontaneous termination of AF in isolated canine atrium (reproduced with permission from [5]). B) The above experiment is simulated with our human atrial myocyte model. The cell is paced rapidly (10 Hz) for 20 s and then returned to sinus rhythm (1 Hz) in the presence of 1 µM ACh. Time courses of E_m (top) and intracellular Ca²⁺ concentration ([Ca²⁺]_i, bottom) are shown. C) Sequence of simulated beats after returning to normal sinus rhythm. AP progressively shortens (left) due to SR unloading, and diminishes Ca²⁺ transient (right) and I_NCX.