Na+/Ca2+ exchanger (sodium-calcium exchanger , NCX) is an antiporter membrane protein that removes calcium from cells. It uses the energy that is stored in the electrochemical gradient of sodium (Na+) by allowing Na+ to flow down its gradient across the plasma membrane in exchange for the countertransport of calcium ions (Ca2+). Na+/Ca2+ exchanger removes a single calcium ion in exchange for the import of three sodium ions. Na+/Ca2+ exchanger exists in many different cell types and animal species. Na+/Ca2+ exchanger is considered one of the most important cellular mechanisms for removing Ca2+. The Na+/Ca2+ exchanger does not bind very tightly to Ca2+ (has a low affinity), but it can transport the ions rapidly (has a high capacity), transporting up to five thousand Ca2+ ions per second. The Na+/Ca2+ exchanger also likely plays an important role in regaining the cell's normal calcium concentrations after an excitotoxic insult.