What Is Ventricular Action Potential?

Ventricular muscle cell action potentials are divided into five phases, which are composed of depolarization and repolarization processes.

Ventricular myocyte action potential

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Ventricular myocyte action potentials are divided into five phases,

1: 0 (depolarization process)-ventricular depolarization process,

: After the ventricular myocyte depolarization reaches its peak, repolarization begins immediately. The repolarization process is relatively slow and is divided into 4 phases:

1) Phase 1 (Initial phase of rapid repolarization): After the depolarization of the myocardial cell reaches its peak, the cardiomyocyte membrane potential drops rapidly from the original + 30mV to 0mV, and the spike potential is formed with the phase 0 depolarization.
The mechanism is: the permeability of the myocardial cell membrane to sodium ions decreases rapidly, coupled with the closure of fast sodium channels, sodium ions stop flowing inward. At the same time, potassium ions in the membrane quickly flow out, causing a potential difference between the membrane and the exterior, forming a spike potential with phase 0.

2) Phase 2 (platform phase): The membrane potential repolarizes slowly and the potential is close to the 0mV level, so it becomes the plateau phase. The plateau is a period unique to the myocardium.

The mechanism is: mainly due to the slow inflow of calcium ions and the slow outflow of a small amount of potassium ions. There is a voltage-gated slow calcium channel on the myocardial cell membrane, which is activated when the myocardial membrane is depolarized to -40mV, and it appears to be continuously open after stage 0. The slow inward flow of calcium ions into the membrane along the concentration gradient makes the membrane tend to depolarize. In the early plateau phase, the amount of positive charges across the membrane carried by the inflow of calcium ions and the outflow of potassium ions, etc., and the membrane potential is stable at stage 1. 0mV level reached by repolarization. Subsequently, the calcium ion channel was gradually deactivated, potassium ions outflow gradually increased, the positive charge amount outside the membrane gradually increased, a potential difference formed inside and outside the membrane, and a late plateau was formed.

3) Phase 3 (the end of rapid repolarization): the potential in the membrane gradually decreases from 0mV to -90mV, completing the repolarization process.
The mechanism is: After the plateau phase, the calcium ion channel is inactivated, and the calcium ion stops influx. At this time, the permeability of the myocardial cell membrane to potassium ion recovers and increases, the potassium ion quickly flows out, and the membrane potential returns to the resting potential to complete repolarization. process. During this period, the repolarization process of each cell in the ventricle is different, which causes the potential difference between the repolarized area and the unrepolarized area, and also promotes the repolarization process in the unrepolarized area. Therefore, the development of phase 3 repolarization is very rapid.

4) Phase 4 (resting period): This period is the period after the membrane repolarization is completed and the membrane potential recovers and stabilizes at -90mV.
The mechanism is: through the sodium-potassium pump and calcium-sodium ion exchange, the inwardly flowing sodium ions and calcium ions are expelled from the membrane, and the outflowing potassium ions are transported into the membrane, so that the ion distribution inside and outside the cell is restored to a resting state Levels, thereby maintaining normal excitability of myocardial cells.