Figure 3. Calcium transients and cell shortening triggered by action potentials under conditions of equal SR load.

A, the voltage protocols: control and post-MI APs were applied to myocytes after a loading protocol of eight 100 ms steps to +10 mV. B, representative Ca²⁺ transients triggered by the control AP (left) and post-MI AP (right). C, fractional cell shortening associated with the intracellular Ca²⁺ transients triggered by control (left) and post-MI (right) APs. D, peak Ca²⁺ transients (left) are elevated 1.7-fold upon stimulation with a post-MI AP relative to the control AP while fractional cell shortening (right) is increased 3.8-fold. *P < 0.05; **P < 0.005.