Figure 4. Ca²⁺ transient of adult isolated cardiac myocytes from Epac1 KO.

(A and B) Typical recordings of Ca²⁺ transients in cardiac myocytes from WT (A) and Epac1 KO (B). Note that the basal and peak Ca²⁺ transient amplitude and decay rate are smaller in Epac1 KO (n = 32 cells from 4 animals each). (C and D) Ca²⁺ transient parameters of isolated cardiac myocytes from Epac1 KO and WT. The basal Ca²⁺ concentration (WT versus Epac1 KO: 139 ± 6.8 versus 99 ± 11.8 nM) and peak Ca²⁺ concentration (WT versus Epac1 KO: 883 ± 35.3 versus 559 ± 33.2 nM) were significantly lower in Epac1 KO than in WT (C). The decay time constant (τ) was significantly larger in Epac1 KO than in WT (WT versus Epac1 KO: 108 ± 6.6 versus 187 ± 13.2 ms) (n = 32 cells, *P < 0.05) (D). (E and F) Typical recordings of Ca²⁺ transients after caffeine (10 mM) treatment of cardiac myocytes from WT (E) and Epac1 KO (F). (G) Peak Ca²⁺ concentration after caffeine (10 mM) treatment was significantly decreased in Epac1 KO compared with WT (WT versus Epac1 KO: 1210 ± 143 versus 835 ± 87.6 nM, n = 7, *P < 0.05).