The influences of the ionic channel conductances and kinetics on the phase-locking behaviors of modeled sinoatrial node cells and tissue

Sinoatrial node (SAN) is the leading pacemaker of the heart, whose pathologies are closely associated to certain kinds of arrhythmias. Phase-locking is a characteristic behavior of the self-oscillatory SAN system, which is relevant to the heart rate modulation. It is known that the SAN phase-locking properties are influenced by the stimulating magnitude, the stimulated site in the tissue, the intercellular coupling strength and even the couplings from the atrial cells. Besides the above knowledge, a practical problem remains undiscussed, i.e., the influences of the channel conductances and kinetics on the phase-locking property. In the present paper a detailed electrophysiological SAN model is investigated. The effects of several major parameters modulating the channels' conductances and the time constants are illustrated. We find that the phase-locking ranges depend on the automaticity of the system. Any parameter variation slowing down the intrinsic oscillating rate may increase the phase-locking ranges, while that speeding up the rate may shrink them. The well known phase resetting property is applied to explain the phenomena, founding on which the analytical formulas for estimating the phase-locking ranges are derived.