Which statement best describes the action potential of non-pacemaker cardiac cells?

• A. Rapid depolarization with a prolonged plateau phase followed by repolarization
• B. Spontaneous depolarization and repolarization
• C. Resting membrane potential around -60 mV
• D. Rapid repolarization with no plateau

Answer: (A)

Non-pacemaker cardiac cells, such as atrial and ventricular myocytes, have an action potential that starts with a rapid upstroke from a very negative resting potential, then a plateau phase where calcium enters the cell while potassium exits, keeping the membrane depolarized for an extended time, and finally repolarization as calcium channels close and potassium currents dominate. This prolonged plateau after the rapid depolarization is a hallmark of these cells and supports the sustained contraction necessary for pumping. Pacemaker cells instead show automatic diastolic depolarization (spontaneous rise toward threshold) rather than a true plateau, and the resting potential of non-pacemaker cells is much more negative (around -85 to -90 mV) than -60 mV. Describing rapid depolarization with a prolonged plateau followed by repolarization best fits the action potential of non-pacemaker cardiac cells.