SODIUM/POTASSIUM PUMP

• Found in the membrane of all animal cells
• Active transport – uses ATP (around 30% of a cell’s total ATP usage) breaking it down to ADP and phosphate
• Helps maintain membrane voltage (thought to contribute about 10% of total voltage)
• Maintains sodium and potassium concentration gradients
• Helps maintain cellular volute by regulating a cell’s osmolarity
• Transports 3 sodium ions out of the cell and 2 potassium ions into the cell

The sodium and potassium ion gradients set up by the pump are required for numerous functions such as:

• Nerve cell action potentials
• Muscle contractions
• Glucose absorption by intestinal cells

SODIUM/POTASSIUM PUMP CYCLE

1. Intracellular sodium ions bind the protein

2. Protein becomes phosphorylated (phosphate added)

3. Conformational change in the protein due to the phosphorylation ejects the sodium ions to the now accessible extracellular space

4. Extracellular potassium binds to the protein

5. Protein is dephosphorylated (phosphate is removed)

6. Due to dephosphorylation, protein returns to original conformation and ejects the potassium ions intracellularly. The pump is now ready to start the cycle again at step 1.