Sodium-calcium exchanger

solute carrier family 8 (sodium/calcium exchanger), member 1
Identifiers
Symbol	SLC8A1
Alt. symbols	NCX1
Entrez	6546
HUGO	11068
OMIM	182305
RefSeq	NM_021097
UniProt	P32418
Other data
Locus	Chr. 2 p23-p21

solute carrier family 8 (sodium-calcium exchanger), member 2
Identifiers
Symbol	SLC8A2
Entrez	6543
HUGO	11069
OMIM	601901
RefSeq	NM_015063
UniProt	Q9UPR5
Other data
Locus	Chr. 19 q13.2

solute carrier family 8 (sodium-calcium exchanger), member 3
Identifiers
Symbol	SLC8A3
Entrez	6547
HUGO	11070
OMIM	607991
RefSeq	NM_033262
UniProt	P57103
Other data
Locus	Chr. 14 q24.1

The sodium-calcium exchanger (often denoted Na⁺/Ca²⁺ exchanger, NCX, or exchange protein) 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⁺). The NCX removes a single calcium ion in exchange for the import of three sodium ions. The exchanger exists in many different cell types and animal species. The NCX is considered one of the most important cellular mechanisms for removing Ca²⁺.

The exchanger is usually found in the plasma membranes and the mitochondria and endoplasmic reticulum of excitable cells.

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. Therefore, it requires large concentrations of Ca²⁺ to be effective, but is useful for ridding the cell of large amounts of Ca²⁺ in a short time, as is needed in a neuron after an action potential. Thus, the exchanger also likely plays an important role in regaining the cell's normal calcium concentrations after an excitotoxic insult. Another, more ubiquitous transmembrane pump that exports calcium from the cell is the plasma membrane Ca²⁺ ATPase (PMCA), which has a much higher affinity but a much lower capacity. Since the PMCA is capable of effectively binding to Ca²⁺ even when its concentrations are quite low, it is better suited to the task of maintaining the very low concentrations of calcium that are normally within a cell. Therefore, the activities of the NCX and the PMCA complement each other.

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Wikipedia