The two kinds of calcium ATPase are:[2] Plasma membrane Ca2+ ATPase (PMCA) is a transport protein in the plasma membrane of cells that serves to remove calcium (Ca2+) from the cell.

[5] The PMCA and the sodium calcium exchanger (NCX) are together the main regulators of intracellular Ca2+ concentrations.

[6] The PMCA belongs to a family of P-type primary ion transport ATPases that form an aspartyl phosphate intermediate.

It is a Ca2+ ATPase that transfers Ca2+ from the cytosol of the cell to the lumen of the SR at the expense of ATP hydrolysis during muscle relaxation.

This ensures that the cytosolic concentration of free calcium in resting muscle is below 0.1 μM.