Plasma membrane Ca2+ ATPase

The plasma membrane Ca²⁺ ATPase (PMCA) is a transport protein in the plasma membrane of cells and functions to remove calcium (Ca²⁺) from the cell. PMCA function is vital for regulating the amount of Ca²⁺ within all eukaryotic cells. There is a very large transmembrane electrochemical gradient of Ca²⁺ driving the entry of the ion into cells, yet it is very important that they maintain low concentrations of Ca²⁺ for proper cell signalling. Thus, it is necessary for cells to employ ion pumps to remove the Ca²⁺. The PMCA and the sodium calcium exchanger (NCX) are together the main regulators of intracellular Ca²⁺ concentrations. Since it transports Ca²⁺ into the extracellular space, the PMCA is also an important regulator of the calcium concentration in the extracellular space.

PMCAs belong to the family of P-type primary ion transport ATPases which form aspartyl phosphate intermediates.

Various forms of PMCA are expressed in different tissues, including the brain.

The pump is powered by the hydrolysis of adenosine triphosphate (ATP), with a stoichiometry of one Ca²⁺ion removed for each molecule of ATP hydrolysed. It binds tightly to Ca²⁺ ions (has a high affinity, with a K_m 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 concentrations within the cell are very low, so it is suited for maintaining Ca²⁺ at its normally very low levels.Calcium is an important second messenger, so its levels must be kept low in cells to prevent noise and keep signalling accurate. The NCX is better suited for removing large amounts of Ca²⁺ quickly, as is needed in neurons after an action potential. Thus the activities of the two types of pump complement each other.

...
Wikipedia