Calcium-induced calcium release (CICR) describes a biological process whereby
calcium is able to activate calcium release from intracellular Ca
2+ stores (e.g.,
endoplasmic reticulum or
sarcoplasmic reticulum). Although CICR was first proposed for
skeletal muscle
Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...
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 in
cardiac muscle. 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, 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 in myocardium relies on sarcolemma depolarization and subsequent Ca
2+ entry to trigger Ca
2+ release from the
sarcoplasmic reticulum. When an
action potential
An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...
depolarizes the cell membrane, voltage-gated Ca
2+ channels (e.g.,
L-type calcium channels) are activated. CICR occurs when the resulting Ca
2+ influx activates
ryanodine receptors on the
SR membrane, which causes more Ca
2+ 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 Ca
2+ that is important in activating muscle contraction.
References
{{DEFAULTSORT:Calcium-Induced Calcium Release
Muscular system