The plasma membrane Ca2+ ATPase (PMCA) is a transport protein in the plasma membrane of cells responsible for removing calcium (Ca2+) from the cell. This pump is vital for regulating the amount of Ca2+ within cells1.
The PMCA and the Na+ calcium exchanger (NCX) are together the main regulators of intracellular Ca2+ concentrations2.
Since it transports Ca2+ into the extracellular space, the PMCA is also an important regulator of the Ca2+ concentration in the extracellular space3.
The PMCA belongs to a family of P-type primary ion transport ATPases, and is expressed in a variety of tissues, including the brain4.
The pump is powered by the hydrolysis of adenosine triphosphate (ATP), with a stoichiometry of one Ca2+ ion removed for each molecule of ATP hydrolyzed. It binds to Ca2+ ions with a high affinity (a Km of 100 to 200 nM) but does not remove Ca2+ at a very fast rate. This is in contrast to the NCX, which has a low affinity and a high capacity. Thus, the PMCA is effective at binding Ca2+ even when its concentration within the cell is very low, so it is suited for maintaining Ca2+ at its normally very low levels. The NCX is better suited for removing large amounts of Ca2+ quickly, as it is needed in neurons after an action potential. Thus the activities of the two types of pump complement each other5.
