(A) Epac-induced wave of elevated cytosolic [Ca²⁺] ([Ca²⁺]_i) shown in 41.0 × 20.5 µm confocal microscope fluo-3 images taken in successive 65 ms intervals within isolated ventricular myocyte. (B, C) Families of loose-patch clamp ionic current densities in a ventricular preparation; pulse protocol investigating Na⁺ channel activation and inactivation as in Figure 5A. Na⁺ currents in response to (B) activation by depolarization to level V₁ and (C) following their inactivation, to final level V₂ following their inactivation at level V₁. Recordings made (a) before pharmacological challenge, (b) in the presence of 8-CPT (1 µM) alone or (c) following further addition of dantrolene, (d) after adding dantrolene alone or (e) combined with 8-CPT. (D) Corresponding dependences of Na⁺ current activation (top row) and inactivation (bottom row) (mean ± SEM) upon voltage V₁ (a) before (open squares) and following introduction of 8-CPT (filled triangles) and 8-CPT and dantrolene combined (filled circles), (b) before (open squares) and following introduction of dantrolene (filled diamonds), (c) before (open squares) and following introduction of a combination of 8-CPT and dantrolene (filled circles).((A) From Figure 8 by permission (Hothi et al. [45]); (B), (C) from Figure 2 and (D) from Figure 4 by permission (Valli et al. [76]).