How would you describe the resting state of non-pacemaker versus pacemaker cells?

• A. Non-pacemaker cells have a true resting potential; pacemaker cells do not
• B. Both have a resting potential
• C. Pacemaker cells have a stable resting potential; non-pacemaker do not
• D. Neither have a resting potential

Answer: (A)

Non-pacemaker (contractile) cells and pacemaker (automatic) cells differ in their resting electrical state. Contractile cells sit at a true resting membrane potential between beats, around -85 to -90 mV, maintained mainly by a high potassium conductance and minimal inward currents at rest. This stable potential is what allows a well-defined action potential to be triggered when the cell is stimulated.

Pacemaker cells, however, do not hold a fixed resting voltage. After an action potential, they experience a diastolic depolarization—the pacemaker potential—driven by a funny current (If) through HCN channels and a gradual influx of Na+ and Ca2+ as the membrane potential slowly drifts upward toward threshold. This continuous drift means there isn’t a true resting potential; instead the membrane potential slowly depolarizes until it reaches the threshold to fire another action potential.

That’s why the statement describing non-pacemaker cells as having a true resting potential while pacemaker cells do not best captures the distinction: contractile cells maintain a stable resting potential, whereas pacemaker cells do not.