A, Representative caffeine-induced Ca2+ transient traces. B, Average Δ [Ca2+]i for caffeine-induced Ca2+ transients (SR Ca2+ load). *P<0.05 vs. WT. # P<0.05 vs. CaMKII-TG. C, Average rate constant kCa for [Ca2+]i decline during caffeine exposure (which indicates NCX activity). *P<0.05 vs. WT. **P<0.01 vs. WT. The number of cells studied: WT n=6, PLN-KO n=21, CaMKII-TG n=9, and KO/TG n=9.