Calcium pumps are a family of

ion transporter In biology, a transporter is a transmembrane protein that moves ions (or other small molecules) across a biological membrane to accomplish many different biological functions including, cellular communication, maintaining homeostasis, energy produc ...

s found in the

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

of all animal cells. They are responsible for the

active transport In cellular biology, ''active transport'' is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellul ...

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

out of the cell for the maintenance of the steep Ca²⁺

electrochemical gradient An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the chemical gradient, or difference in solute concentration across a membrane, and th ...

across the cell membrane. Calcium pumps play a crucial role in proper

cell signalling In biology, cell signaling (cell signalling in British English) or cell communication is the ability of a cell to receive, process, and transmit signals with its environment and with itself. Cell signaling is a fundamental property of all cellula ...

by keeping the intracellular calcium concentration roughly 10,000 times lower than the extracellular concentration. Failure to do so is one cause of muscle

cramp A cramp is a sudden, involuntary, painful skeletal muscle contraction or overshortening associated with electrical activity; while generally temporary and non-damaging, they can cause significant pain and a paralysis-like immobility of the aff ...

s. The plasma membrane Ca²⁺ ATPase and the

sodium-calcium exchanger The sodium-calcium exchanger (often denoted Na+/Ca2+ exchanger, exchange protein, or NCX) is an antiporter membrane protein that removes calcium from cells. It uses the energy that is stored in the electrochemical gradient of sodium (Na+) by al ...

are together the main regulators of

intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

Ca²⁺ concentrations.

Biological role

Ca²⁺ has many important roles as an intracellular messenger. The release of a large amount of free Ca²⁺ can trigger a

fertilized egg A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

to develop,

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

cells to contract,

secretion 440px Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical ...

by secretory cells and interactions with Ca²⁺ -responsive proteins like

calmodulin Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bind ...

. To maintain low concentrations of free Ca²⁺ in the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

, cells use membrane pumps like calcium ATPase found in the membranes of

sarcoplasmic reticulum The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other Cell (biology), cells. The main function of the SR is to store calcium ions (Ca2+). Calcium in bio ...

. These pumps are needed to provide the steep

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.

Crystallography of calcium pumps

The structure of calcium pumps found in the sarcoplasmic reticulum of skeletal muscle was elucidated in 2000 by Toyoshima, et al. using microscopy of tubular crystals and 3D microcrystals. The pump has a molecular mass of 110,000 amu, shows three well separated cytoplasmic domains, with a transmembrane domain consisting of ten

alpha helices The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...

and two transmembrane Ca²⁺

binding sites In biochemistry and molecular biology, a binding site is a region on a macromolecule such as a protein that binds to another molecule with specificity. The binding partner of the macromolecule is often referred to as a ligand. Ligands may inclu ...

Mechanism

Classical theory of active transport for P-type ATPases Data from crystallography studies by Chikashi Toyoshima applied to the above cycle

References

{{Reflist, 2 Cell biology Transport proteins nl:Sarcolemmale calciumpomp