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. Author manuscript; available in PMC: 2016 Dec 1.
Published in final edited form as: Circ Arrhythm Electrophysiol. 2015 Sep 25;8(6):1472–1480. doi: 10.1161/CIRCEP.115.003085

Figure 3.

Figure 3

[Na]i clamping abolishes the EAD on-off switch and unmasks bistability. A. Clamping [Na]i (at 8.8 mM) during either no EAD (black) or EAD phase (red) eliminates oscillations in both APD (B) and [Ca]i (C). The phase at the time of [Na]i-clamp dictates the new stable steady-state APD and [Ca]i. D. A supra-threshold perturbation (inward current injection, -7.7 A/F for 1 ms, during the AP plateau of 5th beat, arrow) succeeds (red), whereas a 1.2% smaller perturbation fails (black) to switch APD from short to long steady-state. E. Long (with EAD) and short APs (without EAD) coexist over a range of [Na]i. Switches between long and short APDs (arrows) occur at different [Na]i, revealing hysteresis. F. Bistability and hysteresis in diastolic [Ca]i.