Analyses of the Ca²⁺ transient and its sequestration by SERCA in RVCM and LVCM. (A) Under the whole-cell voltage-clamp configuration containing fura-2, repetitive AP-triggering current injections (∼1.0 nA, 6 ms, 1 Hz) were applied. The stimulus was halted after confirming the steady-state responses, and fast perfusion of caffeine (20 mM) was applied to evoke caffeine-induced Ca²⁺ transient. After the caffeine treatment, the APs were triggered again, which induced the recovery of Ca²⁺ transient. Then, the bath was perfused with 0 Na/0 Ca solution, followed by the fast transient perfusion of caffeine (20 mM, 1 s). (B) The time constants (τ_tran, τ_caff, and τ_0Na0Ca) were obtained by fitting the decaying phase of Ca²⁺ transients using single exponential function. (C–E) Summary of the time constants (τ_tran, τ_caff, and τ_0Na0Ca). The τ_tran and τ_0Na0Ca were longer in RVCM, while τ_caff was not different in the two ventricles (n = 7, n = 5). (F) The relative rate constants reflecting the relative contributions of Ca²⁺-removal mechanisms are summarized. The relative rate of total Ca²⁺ removal and SERCA activity are significantly lower in RVCM (P < 0.0001). All statistical tests performed using Student’s t test. ***, P < 0.001.