Why Cells Need Calcium Pumps
Ca2+ has many important roles as an intracellular messenger. The release of a large amount of free Ca2+ can trigger a fertilized egg to develop, skeletal muscle cells to contract, secretion by secretory cells and interactions with Ca2+ -responsive proteins like calmodulin. To maintain low concentrations of free Ca2+ in the cytosol, cells use membrane pumps like calcium ATPase found in the membranes of sarcoplasmic reticulum of skeletal muscle. These pumps are needed to provide the steep electrochemical gradient that allows Ca2+ to rush into the cytosol when a stimulus signal opens the Ca2+ channels in the membrane. The pumps are also necessary to actively pump the Ca2+ back out of the cytoplasm and return the cell to its pre-signal state.
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