Fig. 3.

Ca²⁺ handling properties and Ca²⁺-related alternans

(a) Schematic of the ventricular intracellular Ca²⁺ handling components and the main ionic currents involved in depolarization and repolarization (I _Na: fast Na⁺ current; I _to: transient outward K⁺ current; I _Kr: rapid delayed rectifier K⁺ current; I _Ks: slow delayed rectifier K⁺ current; I _K1: time-independent K⁺ current; I _NCX: Na⁺-Ca²⁺ exchange current; I _NaL: late Na⁺ current; I _CaL: L-type Ca²⁺ channel (LCC) current; I _up: pump current; I _leak: leak current; I _RyR: ryanodine receptor current; J _xfer: Ca²⁺ flux transferred from subspace to the cytosol). (b) Illustration of positive and negative Ca²⁺→voltage couplings. Positive (negative) coupling refers to the case that a larger Ca²⁺ transient is accompanied with a longer (shorter) APD during the same beat at a constant CL. (c) Experimentally measured fractional SR Ca²⁺ release as a function of [Ca²⁺]_SRT (total Ca²⁺ content in SR), reproduced with permission from Shannon et al. (2000). (d) Simulated fractional SR Ca²⁺ release from our work (Zang et al., 2013). [Ca²⁺]_JSR,t: total Ca²⁺ content in junctional SR (JSR)