Calcium concentration microdomains (CCMs) are sites in a cell's

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

with a localised high

calcium ion 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 ...

(Ca²⁺) concentration. They are found immediately around the intracellular opening of

calcium channel A calcium channel is an ion channel which shows selective permeability to calcium ions. It is sometimes synonymous with voltage-gated calcium channel, although there are also ligand-gated calcium channels. Comparison tables The following tables e ...

s; when a calcium channel opens, the Ca²⁺ concentration in the adjacent CCM increases up to several hundred

micromolar Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of sol ...

(μM). These microdomains take part in calcium signaling, which has a diverse range of potential outcomes. Calcium concentration microdomains can be visualised with fluorescence microscopy by using

aequorin Aequorin is a calcium-activated photoprotein isolated from the hydrozoan ''Aequorea victoria''. Its bioluminescence was studied decades before the protein was isolated from the animal by Osamu Shimomura in 1962. In the animal, the protein occurs ...

as a reporter protein.

Ion Channel Process

The actions of the Na-K-ATPase enzyme relate with the creation of calcium-signaling microdomains. Na-K-ATPase is a protein that pumps Na⁺ and K⁺ across the cell membrane. Na-K-ATPase helps to keep the body at equilibrium by the movement of those ions through the plasma membrane. This ion pump helps to reset the movement of ions during an

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

by sending K⁺ into the cell and sending Na⁺ out of the cell. Since it opposes the normal flow of ions during an action potential, energy in the form of ATP (

adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms of ...

) is used. Calcium is also regulated using this Na-K-ATPase due to the enzyme's interactions with protein and non-protein molecules. The main interaction that keeps calcium regulated is the binding of Na-K-ATPase to inositol 1,4,5-trisphosphate ( IP3). IP3 is a secondary messenger that helps to send neuronal signals through the body. The neuronal cells have the calcium-signaling microdomains in the

right next to the pre- and post-synaptic calcium channels in the nerve cells. Figure 1 is an example of how Na-K-ATPase forms the calcium-signaling microdomain. The

astrocytes Astrocytes (from Ancient Greek , , "star" + , , "cavity", "cell"), also known collectively as astroglia, are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical control of endo ...

which are star-shaped glial cells in the central nervous system are the main cells with these calcium-signaling micro domains. In fact, a rigorous mathematical analysis in

has shown that localized inflow of Ca²⁺ remains localized, despite the diffusion of cytosolic Ca²⁺ and potential storage in the endoplasmic reticulum. A Na⁺/Ca²⁺ exchanger ( NCX) is also involved in regulating the amount of calcium in cells. The NCX switches the intra- and extra-cellular amounts of Na⁺ and Ca²⁺. NCX works together with Na-K-ATPase to create calcium concentration microdomains in certain cells like astrocytes discussed above. Specific forms of Na-K-ATPase, the α2 or α3 isoforms, actually interact with the NCX in the formation of the calcium microdomains in astrocytes.

Ion Channel Process

Neurological Interactions

Astrocytes

Muscular Interactions

Muscle Cells

Footnotes

References