Fig. 6.

Amount of Ca²⁺ (∆[Ca²⁺]_i, µM) that enters into and extrudes from the cytosol via ionic channels and exchangers in ENDO and EPI cells over the duration of the calcium transient (≈500 ms) during an isometric twitch. Numbers show percentage of the values in the ENDO model with respect to the EPI model. Integrals of the following simulated ionic currents and fluxes (i _x) carrying Ca²⁺ are shown: i _CaL Ca²⁺ current via L-type Ca²⁺ channels, i _bCa background Ca²⁺ current, i _NaCa(f) NCX current during the forward mode, i _NaCa(r) NCX current during the reverse mode, i _rel Ca²⁺ release flow from the SR, i _up SERCA pump flow from cytosol to the SR