Which pump maintains the resting membrane potential by moving Na+ out of the cell and K+ into the cell?

• A. Na+/K+ pump
• B. Ca2+ pump
• C. H+/K+ pump
• D. Na+/Ca2+ exchanger

Answer: (A)

Maintaining the resting membrane potential relies on keeping a high Na+ outside and a high K+ inside the cell, a balance that is actively preserved by the Na+/K+ ATPase. This pump uses one ATP to move three Na+ ions out of the cell and two K+ ions into the cell. The unequal exchange helps sustain a negative interior and the ion gradients that underlie excitability: when channels open, Na+ tends to enter and K+ tends to leave, but the pump keeps those gradients from dissipating.

Other pumps handle different tasks if you look at their roles: a Ca2+ pump clears Ca2+ from the cytosol, a H+/K+ pump exchanges H+ and K+ for pH regulation (not mainly about resting potential in most cells), and the Na+/Ca2+ exchanger moves Ca2+ out using the Na+ gradient but does not directly maintain the resting potential by pumping Na+ out and K+ in.