Plateau form of membrane action potential
The cause of membrane action potential plateaus is a combination of many factors. First, in the myocardium, two types of channels memorialize the depolarization process.
In some cases, the excited membrane did not repolarize immediately after depolarization; instead, the membrane potential remained in a plateau near the peak of the potential for about a few milliseconds, and only then just started to repolarize. As indicated in the figure.
Figure. Action potential (in millivolts) from the Purkinje fibres of the heart, plateau form.
Elevated plateaus can be readily seen throughout the depolarization process. This is the type of action potential that occurs in the myocardium, where the plateau lasts if 0.2-0.3 seconds and causes contraction of the myocardium to last for this same length of time.
The cause of the plateau is a combination of many factors. First, in the myocardium, two types of channels memorialize the depolarization process: (1) activated na channels, also called rapid channels, and (2) voltage-activated sodium-activated calcium channels (channels). L-type calcium)- opens slowly and is therefore called a slow channel. The rapid opening of the channel causes a spike in the action potential, while the prolonged opening of the slow calcium-sodium channel mainly allows calcium ions to enter the fibrils, which is largely responsible for the plateau part of the action potential.
The second factor that may be partly responsible for the plateau is that the potential potassium gate channels open more slowly than usual, often not opening much until the end of the plateau. This factor delays the return of the membrane potential to the normal negative value of -80 .
To -90 mV. The plateau ends when the calcium-sodium channels close and permeabilize so that potassium increases.