Figure 3. Electrical, mechanical and Ca²⁺ alternans in cardiac myocytes.

A; Simultaneous recordings of action potentials and cell shortening from a single ventricular myocyte revealing discordant electromechanical alternans. To the right, two action potentials recorded during successive small- (open circle) and large-amplitude (filled circle) shortenings are superimposed to illustrate the differences in duration and kinetics. Modified from Hüser et al. (10) with permission. B; Simultaneous recordings of cytosolic ([Ca²⁺]_i; top) and intra-SR ([Ca²⁺]_SR; bottom) Ca²⁺ alternans from a single ventricular myocyte. C; Simultaneous recordings of [Ca²⁺]_i (top) and I_Ca (bottom) in voltage-clamped atrial myocytes. To the right, an overlay of I_Ca measured during a large-amplitude Ca²⁺ transient (L; blue trace) and a small-amplitude Ca²⁺ transient (S; red trace) shows that Ca²⁺ alternans are not accompanied by alternating peak I_Ca. Modified from Shrkyl et al. (67) with permission.