Phase resetting in central and peripheral sinoatrial node cell models

We characrerite the eflects of external stimulation on central and peripheral sinoatrial node (SAN) celh using the Zhang et al. model [XI. Phase transition curves (PTCs) for brief (0.5ms) depolarizing and hyperpolarising electrical current pulses of varying amplitude and of timing spanning the whole period are obtained. The application of a critical depdarizing 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 con3guration. The peripheral SAN cell does not exhibit a similar singularity and annihilation Of the normal acrivity.