Calcium-induced calcium release (CICR) describes a biological process whereby

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 ...

is able to activate calcium release from intracellular Ca²⁺ stores (e.g.,

endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...

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 cells. The main function of the SR is to store calcium ions (Ca2+). Calcium ion levels are kept ...

). Although CICR was first proposed for

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 ...

in the 1970s, it is now known that CICR is unlikely to be the primary mechanism for activating SR calcium release. Instead, CICR is thought to be crucial for

excitation-contraction coupling Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as ...

cardiac muscle Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that ...

. It is now obvious that CICR is a widely occurring cellular signaling process present even in many non-muscle cells, such as in the insulin-secreting pancreatic

beta cells Beta cells (β-cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets. In patients with Type 1 diabetes, beta-cell mass and function are dimin ...

, epithelium, and many other cells. Since CICR is a positive-feedback system, it has been of great interest to elucidate the mechanism(s) responsible for its termination.

Examples in biology

Excitation-contraction coupling

Excitation-contraction coupling Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as ...

in myocardium relies on sarcolemma depolarization and subsequent Ca²⁺ entry to trigger Ca²⁺ release from the

. When 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, ...

depolarizes the cell membrane, voltage-gated Ca²⁺ channels (e.g.,

L-type calcium channel The L-type calcium channel (also known as the dihydropyridine channel, or DHP channel) is part of the high-voltage activated family of voltage-dependent calcium channel. "L" stands for long-lasting referring to the length of activation. This c ...

s) are activated. CICR occurs when the resulting Ca²⁺ influx activates

ryanodine receptor Ryanodine receptors (RyR for short) form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons. There are three major isoforms of the ryanodine receptor, which are found in different tiss ...

s on the SR membrane, which causes more Ca²⁺ to be released into the cytosol. In cardiac muscle, the result of CICR is observed as a spatio-temporally restricted Ca²⁺ spark. The result of CICR across the cell causes the significant increase in cytosolic Ca²⁺ that is important in activating muscle contraction.

References

{{DEFAULTSORT:Calcium-Induced Calcium Release Muscular system