Fig. 5.

Sarcoplasmic reticulum (SR) Ca²⁺ content and Ca²⁺ transport rate assessments in isolated cardiomyocytes after MI. Ca²⁺ transients were evoked by 10 mM caffeine in ventricular myocytes from the sham group, MI group, and MI + EC-Exo group on day 28 after MI or sham surgery. A Representative traces of Ca²⁺ transient during caffeine-induced contraction in 0 Na⁺/0 Ca²⁺ Tyrode’s solution or normal Na⁺/Ca²⁺ Tyrode’s solution (NT). B Quantification of the amplitude of caffeine-induced Ca²⁺ transients in 0 Na⁺/0 Ca²⁺ Tyrode’s solution. C Rate constant of SERCA-mediated Ca²⁺ transport (the difference between the rate constant of caffeine-evoked Ca²⁺ transients and electric stimulation-evoked Ca²⁺ transients in NT solution). D Maximum upstroke velocity (V_max) of caffeine-induced Ca²⁺ transient in 0 Na⁺/0 Ca²⁺ Tyrode’s solution. E Rate constant of Na⁺/Ca²⁺ exchanger-1 (NCX-1)-mediated Ca²⁺ transport (the difference between delay rate constant of caffeine-evoked Ca²⁺ transients in NT solution and in 0 Na⁺/0 Ca²⁺ solution). F SERCA activity was accessed using a Ca²⁺-pump ATPase enzyme assay kit. Quantitative data are presented as mean ± SEM. A total of 40–44 cardiomyocytes from four different hearts were measured in each group. Significance was evaluated via one-way ANOVA followed by Tukey’s post hoc test in (B–F). **p < 0.01