Figure 14.

Alternans control induces subcellular alternans in an isolated ventricular myocyte. (A) Alternans control causes a steady-state, period-2 APD (first black trace), and whole-cell Ca²⁺-alternans (second black trace) to transition to a period-1 rhythm. Concurrently, the spatially homogenous Ca²⁺-alternans transitions to a 2-node subcellular alternans. Blue, green, and red traces are the average fluorescence from the three regions diagrammed. (B) Recorded fluorescence frames at the time of maximum calcium concentration in two successive beats during initial control (1), during the transition (2), and at nearly period-1 control (3); beat pairs are marked by gray shaded regions in (A). (C) Ca²⁺-alternans magnitude along the length of the cell is plotted for the experiment shown in (A). For this panel, fluorescence data are binned into 12 adjacent regions perpendicular to the length of the cell and the average Ca²⁺-alternans magnitude (Δc) is plotted for each region for the 25 beats shown (arbitrary fluorescence units), with colors corresponding to the regions diagrammed in (A). Fluorescence data from the extreme ends of the cell are excluded due to motion artifact. Experiments shown are from a cell paced at a cycle length of 300 ms (with alternans control). Adapted from Gaeta et al. (2009).