Phase resetting in central and peripheral sinoatrial node cell models

We characterize the effects of external stimulation on central and peripheral sinoatrial node (SAN) cells using the Zhang et al. model [1]. Phase transition curves (PTCs) for brief (0.5 ms) depolarizing and hyperpolarising electrical current pulses of varying amplitude and of timing spanning the whole period are obtained. The application of a critical depolarizing stimulus (about 0.4 nA) during the late repolarization phase of the action potential resulted in annihilation of activity in central SAN cells, revealing the existence of a stable singularity in the corresponding model configuration. The peripheral SAN cell does not exhibit a similar singularity and annihilation of the normal activity.