Global bifurcation structure and variability of pacemaker rhythm in a detailed model of cardiac sinoatrial node cells

As a cardiac pacemaker, the sinoatrial node spontaneously generates periodic electrical signals (action potentials) in its cells. The action potential generation is deeply related to various ion channels in cell membranes, and abnormalities of the ion channels cause sinus arrhythmia. We use the Zhang model of sinoatrial node cells to investigate the relation between the pacemaker rhythm (frequency of action potential generation) and ion channels. The Zhang model is described by the Hodgkin–Huxley nonlinear ordinary differential equations, and its parameter values vary between the periphery and center cells of the sinoatrial node. We analyze the bifurcation structure of the Zhang model and investigate the variability of the pacemaker rhythm and its sensitivity to ion channel conductance changes for both periphery and center cells. These results are also compared with the previous results of another sinoatrial node cell model: the Yanagihara–Noma–Irisawa model.