During the plateau phase (phase 2) of the ventricular action potential, the membrane potential is maintained near 0 mV primarily because of a balance between which two ion currents?

• A Inward L-type Ca²⁺ current and outward slow K⁺ current (IKs)
• B Inward L-type Ca²⁺ current and outward rapid K⁺ current (IKr) ✓
• C Inward L-type Ca²⁺ current (ICaL) and outward transient K⁺ current (Ito)
• D Inward persistent Na⁺ current and outward IK1 current

Explanation

Phase 2 plateau arises because a sustained inward L-type Ca²⁺ current (ICaL) is balanced by the outward rapid delayed-rectifier K⁺ current (IKr). IKs contributes to phase 3 repolarisation rather than sustaining the plateau. Ito is responsible for the early rapid repolarisation notch (phase 1), not the plateau. Loss-of-function IKr mutations underlie acquired long-QT syndrome type 2.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.