Na+/Ca2+ Exchanger (Na+/Ca2+交换体)

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.