FIGURE 3.
Cardiac cellular electrophysiology modeling approaches. A: general equation representing the change in membrane potential (VM) used to simulate the cardiac action potential as the product of the inverse of membrane capacitance (CM) and the sum of all ion currents (IX). The second equation shows the 3 major components determining the magnitude of an ion current IX. B: most commonly used approaches to model the open probability of a cardiac ion channel. Instantaneous models are direct functions of VM, whereas Hodgkin–Huxley and Markov models are controlled by independent or connected ordinary differential equations (ODEs), respectively. 0K1, 0Na and 0X represent the open probability of the inward-rectifier K+ channel, Na+ channel, and a hypothetical ion channel, respectively, and are determined directly by VM, by the product of an activation gate (m) and an inactivation gate (h), or by a set of coupled ODEs connecting closed (CX), open (OX) and blocked (BX) states. C: emerging approaches for modeling channel gating based on protein structures. C was adapted from Refs. 75 and 76, with permission from Proceedings of the National Academy of Sciences USA and Biophysical Journal, respectively.