Action potentials and Ca2+ transients. (A) Steady-state model APs for CLs of 500 ms (shaded line), 1000 ms (solid line), 2000 ms (shaded dashed line), and 4000 ms (black dashed line). (B) Cytosolic Ca2+ transients corresponding to the APs of A. (C) Mean subspace (dyadic) Ca2+ transient (dashed line) demonstrates that microdomain Ca2+ levels reach significantly higher levels than that in the cytosol (solid line) during the AP at 1000 ms CL. (D) Properties of ICaL (solid line) during the AP at 1000 ms CL, demonstrating relatively strong Ca2+-dependent inactivation (pnot_CDI, shaded line) but weak voltage-dependent inactivation (pnot_VDI, dashed line).