calcium (Ca) pump

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calcium (Ca) pump

one of many similar molecular complexes embodying ion-binding sites and an ATPase in the surface membrane of many cell types, including smooth and cardiac muscle, and in the membrane of the sarcoplasmic reticulum (SR) in skeletal muscle. The pumps actively transport calcium ions (Ca2+) out of the cytoplasm; those in the surface membrane return them to the extracellular fluid, and those in SR membrane return them to within the SR. All use energy derived from hydrolysis of ATP.