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A calcium spark is the microscopic release of calcium (Ca 2+) from a store known as the sarcoplasmic reticulum (SR), located within muscle cells. [1] This release occurs through an ion channel within the membrane of the SR , known as a ryanodine receptor (RyR) , which opens upon activation. [ 2 ]
The release of calsequestrin-bound calcium (through a calcium release channel) triggers muscle contraction. The active protein is not highly structured, more than 50% of it adopting a random coil conformation. [2] When calcium binds there is a structural change whereby the alpha-helical content of the protein increases from 3 to 11%. [2]
Depiction of smooth muscle contraction. Muscle contraction is the activation of tension-generating sites within muscle cells. [1] [2] In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as when holding something heavy in the same position. [1]
Calcium is a ubiquitous second messenger with wide-ranging physiological roles. [2] These include muscle contraction , neuronal transmission (as in an excitatory synapse ), cellular motility (including the movement of flagella and cilia ), fertilization , cell growth (proliferation), neurogenesis , learning and memory as with synaptic ...
This increases calcium release from the SR, increasing the rate of contraction. [16] Therefore, in cardiac muscle, activation of PKA, through the cyclic AMP pathway, results in increased muscle contraction (via RyR2 phosphorylation) and increased relaxation (via phospholamban phosphorylation), which increases heart rate.
However, dysfunction within these Ca 2+-activated pathways can lead to an increase in tone caused by unregulated smooth muscle contraction. This type of dysfunction can be seen in cardiovascular diseases, hypertension, and diabetes. [42] Calcium coordination plays an important role in defining the structure and function of proteins.
There are several mechanisms directly linked to the terminal cisternae which facilitate excitation-contraction coupling. When excitation of the membrane arrives at the T-tubule nearest the muscle fiber, a dihydropyridine channel (DHP channel) is activated. [2] This is similar to a voltage-gated calcium channel, but is not actually an ionotropic ...
When these cells are depolarized, the L-type calcium channels open as in smooth muscle. In skeletal muscle, the actual opening of the channel, which is mechanically gated to a calcium-release channel (a.k.a. ryanodine receptor, or RYR) in the sarcoplasmic reticulum (SR), causes opening of the RYR.