Restoring Resting Membrane Potential

Na+ / K+ ATPase: How does it restore resting membrane potential?

The Na+/K+ ATPase, also known as the sodium-potassium pump, plays a fundamental role in restoring and maintaining the resting membrane potential of cells. It is an integral membrane protein found in the plasma membrane of all animal cells and functions to transport sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, against their electrochemical gradients.

Here’s a detailed explanation of how the Na+/K+ ATPase works to restore the resting membrane potential:

1. Pump activation: The Na+/K+ ATPase consists of three sodium-binding sites and two potassium-binding sites. When the pump is not bound to any ions, it has a high affinity for sodium ions. Sodium ions from the cytoplasm of the cell bind to the sodium-binding sites of the pump.

2. ATP hydrolysis: The Na+/K+ ATPase utilizes the energy derived from the hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) in order to pump ions across the membrane. ATP binds to the pump and undergoes hydrolysis, resulting in the release of a phosphate group (Pi) and the generation of energy.

3. Sodium extrusion: The energy released from ATP hydrolysis causes a conformational change in the pump, leading to the release of the sodium ions to the outside of the cell. This step is known as the extrusion of sodium, whereby three sodium ions are pumped out for every two potassium ions brought in. This extrusion of sodium is crucial for maintaining the low concentration of sodium ions inside the cell.

4. Potassium influx: After releasing the sodium ions, the pump becomes more receptive to potassium ions. Two potassium ions from the extracellular environment bind to the pump’s potassium-binding sites.

5. Pump reset: Once the potassium ions are bound, the pump undergoes another conformational change, returning to its original shape. This resets the pump, making it ready to undergo another cycle of ion transport.

The net effect of the Na+/K+ ATPase is the extrusion of three positively charged sodium ions out of the cell for every two positively charged potassium ions brought into the cell. This movement of ions leads to the restoration of the electrochemical gradients of sodium and potassium across the cell membrane, which is vital for the generation and propagation of action potentials in neurons, as well as various other cellular processes.

Overall, the Na+/K+ ATPase actively maintains the resting membrane potential by contributing to the negative charge inside the cell and the positive charge outside of it. This electrochemical gradient is essential for proper cellular signaling and the overall functioning of excitable cells.

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