calcium:sodium antiporter activity involved in regulation of cardiac muscle cell membrane potential

Definition

Target type: molecularfunction

Enables the transfer of a solute or solutes from one side of a membrane to the other according to the reaction: Ca2+(in) + Na+(out) = Ca2+(out) + Na+(in), which contributes to regulating the membrane potential of a cardiac muscle cell. [GOC:BHF, GOC:mtg_cardiac_conduct_nov11]

Calcium:sodium antiporter activity involved in regulation of cardiac muscle cell membrane potential is a crucial process in maintaining the electrical excitability and contractility of the heart. This transmembrane protein facilitates the exchange of calcium and sodium ions across the plasma membrane of cardiac muscle cells, playing a key role in regulating the membrane potential and action potential propagation.

**Molecular Mechanism:**

The calcium:sodium antiporter, also known as the NCX (sodium-calcium exchanger), operates through a coupled transport mechanism. It utilizes the electrochemical gradient of sodium ions (Na+) to drive the extrusion of calcium ions (Ca2+) from the cell. This process involves the following steps:

1. **Binding of Na+:** The antiporter binds three sodium ions from the extracellular space.
2. **Binding of Ca2+:** Simultaneously, the antiporter binds one calcium ion from the intracellular space.
3. **Conformation Change:** The binding of sodium and calcium ions induces a conformational change in the protein, facilitating the transport of both ions across the membrane.
4. **Release of Ions:** The antiporter releases the sodium ions into the intracellular space and the calcium ion into the extracellular space.

**Regulation of Cardiac Muscle Cell Membrane Potential:**

The calcium:sodium antiporter plays a vital role in regulating the membrane potential of cardiac muscle cells by:

1. **Calcium Extrusion:** Removing calcium ions from the cytoplasm reduces the intracellular calcium concentration, contributing to repolarization of the membrane potential after an action potential.
2. **Sodium Influx:** The inward movement of sodium ions helps to maintain the sodium gradient, which is essential for the function of other membrane transporters, including the sodium-potassium pump.
3. **Action Potential Duration:** The activity of the calcium:sodium antiporter can influence the duration of the action potential, affecting the rate and rhythm of heart contractions.

**Cardiac Function:**

The precise regulation of calcium:sodium antiporter activity is critical for normal heart function. Dysregulation of this transporter can lead to various cardiac disorders, including:

1. **Arrhythmias:** Irregular heartbeats caused by disturbances in the electrical activity of the heart.
2. **Heart Failure:** Reduced ability of the heart to pump blood effectively.
3. **Cardiac Hypertrophy:** Enlargement of the heart muscle.

In summary, calcium:sodium antiporter activity is a fundamental process in regulating the electrical excitability and contractility of the heart. Its precise operation is crucial for maintaining normal cardiac function.'
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Proteins (1)

Compounds (1)