Mechanisms for Changing Pacemaker Cell Automaticity:

Hyperpolarize/hypopolarize overdrive suppression
Alteration of slope (rate of rise) of pre-potential (diastolic potential)
Alteration of threshold; e.g. epinephrine increases gCa⁺⁺ (hypopolarizes), acetylcholine increases gK⁺ (hyperpolarizes)