During the ventricular action potential, which phase is the plateau phase associated with Ca2+ influx?

During the ventricular action potential, which phase is the plateau phase associated with Ca2+ influx?

• A. Phase 0 rapid Na+ influx
• B. Phase 2 plateau Ca2+ influx
• C. Phase 1 initial repolarization
• D. Phase 3 repolarization

Answer: (B)

The plateau is produced by a sustained inward calcium current. After the rapid depolarization, L-type voltage-gated calcium channels open and let Ca2+ enter the cell, opposing the outward potassium currents. This keeps the membrane potential in a depolarized, relatively stable range for a brief period, creating the plateau. The continued Ca2+ entry also triggers calcium release from the sarcoplasmic reticulum to drive contraction. Once the calcium influx wanes and potassium efflux dominates, repolarization resumes. Other phases are driven by different ions: rapid Na+ influx for the initial spike, a brief early repolarization, and then the main repolarization as K+ currents prevail.

The plateau is produced by a sustained inward calcium current. After the rapid depolarization, L-type voltage-gated calcium channels open and let Ca2+ enter the cell, opposing the outward potassium currents. This keeps the membrane potential in a depolarized, relatively stable range for a brief period, creating the plateau. The continued Ca2+ entry also triggers calcium release from the sarcoplasmic reticulum to drive contraction. Once the calcium influx wanes and potassium efflux dominates, repolarization resumes. Other phases are driven by different ions: rapid Na+ influx for the initial spike, a brief early repolarization, and then the main repolarization as K+ currents prevail.