Question

How do cardiac cells sustain a membrane potential of around 0 mV during the plateau phase?

A-increased membrane permeability to potassium ions
B-increased membrane permeability to sodium ions
C-decrease in the amount of calcium diffusing across the membrane
D-calcium channels remain open"

Answer 1

Cardiac cells maintain a membrane potential near 0 mV during the plateau phase as calcium channels remain open, allowing calcium entry that balances potassium leaving the cell, until repolarization occurs.

Step-by-step explanation:

Cardiac cells sustain a membrane potential of around 0 mV during the plateau phase through D-calcium channels remain open. During this phase, the slow Ca2+ channels allow calcium ions (Ca2+) to enter the cell, maintaining a balance against the few K+ channels that are open, which permits potassium ions (K+) to leave the cell. This prolonged entry of Ca2+ contributes to maintaining the membrane potential close to 0 mV, counterbalancing the movement of K+ out of the cell during the long plateau phase of the cardiac action potential.

Once the membrane potential has stabilized near zero, these Ca2+ channels eventually close and more K+ channels open, leading to repolarization as K+ exits the cell, allowing the membrane potential to drop back to the resting levels. The relatively long plateau phase lasts approximately 175 ms, after which the Ca²+ channels close and potassium channels open, leading to repolarization.