Comparison of single-compartment estimates of SR Ca²⁺ release in mouse and frog fibers stimulated by an AP. The lowermost trace in each panel shows an averaged furaptra Δf_CaD signal obtained from several experiments like that in Fig. 4 (A, mouse, n = 8; B, frog, n = 7); in all experiments, Δf_CaD appeared to be virtually free of movement artifacts. The peak, time of peak, and FDHM of the Δf_CaD traces are 0.154, 4.0 ms and 5.2 ms in A; and 0.149, 5.0 ms, and 10.3 ms in B, respectively. Each Δ[Ca²⁺] trace was calculated from Δf_CaD with Eq. 2. The estimated total amount of released Ca²⁺ (Δ[Ca_T]), which was calculated from Δ[Ca²⁺] with the single-compartment version of the model, is equal to the sum of Δ[Ca²⁺] and (not depicted) Δ[CaDye], Δ[CaATP], Δ[CaTrop], Δ[CaParv], Δ[CaPump], and Δ[CaPumped]. Peak Δ[Ca_T] is 380 µM in A and 422 µM in B. The top traces show estimates of the rate of SR Ca²⁺ release. The traces with noise (peak value, 199 µM/ms in A and 172 µM/ms in B) are the derivative of the corresponding Δ[Ca_T] traces. The noise-free traces are mathematical representations of these waveforms that satisfy Eq. 3. With these representations, the total release amount, and values of τ1 and τ2 are 380 µM, 1.4 ms, and 0.55 ms in A; and 420 µM, 1.75 ms, and 0.7 ms, respectively, in B. The FDHM of the release waveform is 1.7 ms in A and 2.2 ms in B.