A fast and tiny current as common generator of slow regular pacemaking in brain and heart

Slow pacemaking is a key physiological process in specific excitable cells, yet its underlying mechanisms remain debated. Here we identify a conserved, voltage-dependent pacemaker current that is essential for slow, regular firing in both midbrain dopaminergic neurons and sinoatrial node cells. Conductance-based models incorporating this current reproduce stable pacemaking, requiring a fast-activating, small-amplitude current. This is further confirmed by dynamic-clamp experiments in dopaminergic neurons. Replacing the pacemaker current in a model with a voltage-independent conductance such as the non-selective sodium leak channels fails to sustain slow rhythmicity, highlighting the necessity for an adequate voltage dependence. Our results suggest a novel and shared biophysical mechanism for slow pacemaking in neuronal and cardiac systems