174 12.23 Calcium Functions

Calcium in hydroxyapatite is a major component of bones and teeth.

There are also a number of non-bone functions of calcium. Calcium is an intracellular signaling molecule. Because of this, intracellular calcium is tightly controlled, primarily stored within organelles.

Non-bone functions include:

Neurotransmitter release

Neurotransmitter release is stimulated by the opening of voltage-gated Ca2+ channels. This stimulates the synaptic vesicle to fuse with the axon membrane and release the neurotransmitter into the synapse, as shown below1.

Figure 12.231 Calcium regulates neurotransmitter release2

Muscle contraction

Calcium is released in muscle cells, where it binds to the protein troponin, changes its shape, and removes the tropomyosin blockade of actin active sites so that contraction can occur3. This can be seen in the following animation and figure (same link).

Web Link

Muscle contraction

Hormone release

Calcium acts as an intracellular messenger for the release of hormones, such as insulin. The link below shows how in the beta cells of the pancreas, the opening of voltage-gated calcium channels stimulates the insulin granules to fuse with the beta cell membrane to release insulin.

Web Link

Insulin release

Blood Clotting

As will be discussed more in the vitamin K section, calcium binding to activated Gla proteins is important in the blood clotting cascade.

Figure 12.232 Calcium bind to Gla proteins. Adapted from reference 4

Enzyme regulation

The binding of calcium to calcium-binding proteins also regulates the action of a number of enzymes4.

References & Links

1. Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw’s perspectives in nutrition. New York, NY: McGraw-Hill.

2. http://en.wikipedia.org/wiki/File:Synapse_Illustration_unlabeled.svg

3.http://legacy.owensboro.kctcs.edu/GCaplan/anat/Notes/API%20Notes%20J%20%20Muscle%20Contraction.htm

4. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.

Links

Muscle contraction – http://legacy.owensboro.kctcs.edu/GCaplan/anat/Notes/API%20Notes%20J%20%20Muscle%20Contraction.htm

Insulin release – http://www.dolcera.com/wiki/images/Image11.jpeg

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