2003 Volume 53 Issue 2 Pages 105-123
Individual ion channels or exchangers are described with a common set of equetions for both the sinoatrial node pacemaker and ventricular cells. New experimental data are included, such as the new kinetics of the inward rectifier K+ channel, delayed rectifier K+ channel, and sustained inward current. The gating model of Shirokov et al. (J Gen Physiol 102: 1005–1030, 1993) is used for both the fast Na+ and L-type Ca2+ channels. When combined with a contraction model (Negroni and Lascano: J Mol Cell Cardiol 28: 915–929, 1996), the experimental staircase phenomenon of contraction is reconstructed. The modulation of the action potential by varying the external Ca2+ and K+ concentrations is well simulated. The conductance of ICaL dominates membrane conductance during the action potential so that an artificial increase of Ito, IKr, IKs, or IKATP magnifies ICaL amplitude. Repolarizing current is provided sequentially by IKs, IKr, and IK1. Depression of ATP production results in the shortening of action potential through the activation of IKATP. The ratio of Ca2+ released from SR over Ca2+ entering via ICaL (Ca2+ gain = ∼15) in excitation-contraction coupling well agrees with the experimental data. The model serves as a predictive tool in generating testable hypotheses.