[Sinus node and ionic currents: physiology and regulation]

The physiology of the sinus node is complex. Several currents are involved in spontaneous diastolic depolarisation, the genesis of automatism: the slow and transient calcium currents, the delayed potassium (K) current, and the If current or pacemaker current. In the cellular organisation of the sinus node, there are dominant and latent cells. An intrasinusal pacemaker shift of the dominant pacemaker may be observed under the effect of many extrinsic factors. Positive chronotropic stimuli induce a shift towards the cephalic part of the sinus node, while the negative chronotropic stimuli induce a shift towards the caudal part of the sinus node. All the channels involved are possible pharmacological targets. Sinus node activity may also be extrinsically modified by many pharmacological agents at the unicellular level or at the level of intercellular relationships, combining automatism and conduction.