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The characteristic feature of pacemaker cell action potentials is that they do not have a true resting membrane potential. Unlike non-pacemaker cells, which have a stable resting membrane potential, pacemaker cells have a slowly depolarizing phase that leads to spontaneous action potentials. This unique behavior is primarily due to the presence of ion channels that allow for a gradual influx of sodium and calcium ions, thus enabling these cells to reach the threshold for depolarization without a fully polarized state.

Pacemaker cells, such as those found in the sinoatrial node of the heart, demonstrate this property, which is crucial for their role in automatically generating rhythmical impulses that regulate heart rate. This characteristic makes them essential for maintaining the heart's rhythmic contractions and overall function.

In contrast, the presence of a distinct resting membrane potential, similar phase 3 depolarization as seen in non-pacemaker cells, and the presence of phase 2 are features more aligned with non-pacemaker cardiac myocytes, where stable resting potentials and well-defined phases of the action potential are observable.