Myocardial infarction induces a decrease in SR Ca²⁺ load. (A) Line-scan images of caffeine-evoked intracellular Ca²⁺ transients after field stimulation at 2 Hz in one ventricular myocyte from sham (left) or PMI (right) mice obtained by the application of 10 mmol/liter caffeine. (B) Averaged caffeine-evoked Ca²⁺ transient peak (F/F₀) of myocytes from sham (white bar; n = 43 cells from six animals) and PMI (red bar; n = 21 cells from five animals) mice. (C) Averaged decay time constant of the caffeine-evoked Ca²⁺ transient (34 cells from six sham animals; 13 cells from five PMI animals). (D) Fractional SR Ca²⁺ release during field stimulation at 2 Hz in control myocytes (white bar; n = 36 cells from three animals) and in cells from PMI mice (red bar; n = 20 cells from three animals). (E) Post-rest potentiation (white bar; n = 36 cells from three animals) and in cells from PMI mice (red bar; n = 20 cells from three animals). Error bars represent the SEM. *, P < 0.05; **, P < 0.001 PMI versus sham.