Calcium in biology


Calcium in biology

Calcium (Ca2+) plays a vital role in the anatomy, physiology and biochemistry of organisms and of the cell, particularly in signal transduction pathways. The skeleton acts as a major mineral storage site for the element and releases Ca2+ ions into the bloodstream under controlled conditions. Circulating calcium is either in the free, ionized form or bound to blood proteins such as serum albumin. The hormone secreted by the parathyroid gland, parathyroid hormone, regulates the resorption of Ca2+ from bone.

Vertebrates

Different tissues contain Ca in different concentrations. For instance, Ca2+ (mostly calcium phosphate and some calcium sulfate) is the most important (and specific) element of bone and calcified cartilage.

Ca2+ ions are one of the most widespread second messengers used in signal transduction. They make their entrance into the cytoplasm either from outside the cell through the cell membrane via calcium channels (such as Calcium-binding proteins), or from some internal calcium storages.

The plasma membrane Ca2+ ATPase (PMCA) obtains energy to pump calcium out of the cell by hydrolysing adenosine triphosphate (ATP).

In neurons, voltage-dependent, calcium-selective ion channels are important for synaptic transmission. Levels of intracellular calcium are regulated by transport proteins that remove it from the cell. For example, the sodium-calcium exchanger uses energy from the electrochemical gradient of sodium by pumping calcium out of the cell in exchange for the entry of sodium.

General effects

The effects of calcium in human cells are most frequently specific, meaning different types of cells respond in different ways. However, in certain circumstances their action may be more general.

Ca2+ ions can damage cells if they enter in excessive numbers (for example in the case of excitotoxicity, or overexcitation of neural circuits, which can occur in neurodegenerative diseases or after insults such as brain trauma or stroke). Excessive entry of calcium into a cell may damage it or even cause it to undergo apoptosis or death by necrosis.

One cause of hypercalcemia is hyperparathyroidism.Apart from that, too much calcium can cause dizziness.

pecific effects

Ca2+ entering the cell plasma causes "specific actions" of the cell, depending on the type of cell. For instance, most secretory cells release vesicles with their secretion, muscle cells contract, synapses release synaptic vesicles and go into processes of synaptic plasticity, etc.

Calcium's function in muscle contraction was found as early as 1882 by Ringer and led the way for further investigations to reveal its role as a messenger about a century later. Because its action is interconnected with cAMP, they are called synarchic messengers. Calcium can bind to several different calcium-modulated proteins such as troponin-C (the first one to be identified) or calmodulin. The ions are stored in the sarcoplasmic reticulum of muscle cells.

Calcium acts as one of the primary regulators of osmotic stress (Osmotic shock).

Invertebrates

Some invertebrates use calcium compounds for building their exoskeleton (shells and carapaces) or endoskeleton (echinoderm plates and poriferan calcareous spicules). Many protists also make use of calcium.

Plants

tructural roles

Ca2+ ions are an essential component of plant cell walls and cell membranes, and are used as cations to balance organic anions in the plant vacuole. [cite journal | last = White | first = Philip J. | coauthors = Martin R. Broadley | year = 2003 | title = Calcium in Plants | journal = Annals of Botany | volume = 92 | issue = 4 | pages = 487–511 | url = http://aob.oxfordjournals.org/cgi/content/full/92/4/487 | accessdate = 2006-09-01 | doi = 10.1093/aob/mcg164 | pmid = 12933363] The Ca2+ concentration of the vacuole may reach millimolar levels. The most striking use of Ca2+ ions as a structural element in plants occurs in the marine coccolithophores, which use Ca2+ to form the calcium carbonate plates with which they are covered.

Some plants that accumulate Ca in their tissues, thus making them more firm. Calcium is stored as Ca-oxalate crystals in plastids.

Cell signalling

Ca2+ ions are usually kept at nanomolar levels in the cytosol of plant cells, and act in a number of signal transduction pathways.

=Measuring Ca2+ in living tissue=The total amount of Ca2+ present in a tissue may be measured using atomic absorption spectrometry, in which the tissue is vapourized and combusted. To measure Ca2+ in vivo, a range of fluorescent dyes may be used. These dyes are based on Ca2+-binding molecules such as BAPTA and so care is required in their use, because they may actually buffer the Ca2+ changes which they are used to measure.

=Food sources=The USDA web site has a very complete table of calcium content (in mg) of common foods per common measures (link below).

Calcium amount in foods, 100 g:
* parmesan (cheese) = 1140 mg
* sesame seeds (unhulled) = 989 mg
* milk powder = 909 mg
* molasses = 273 mg
* hazelnuts = 250 mg
* almonds = 234 mg
* nuts = 99 mg
* ricotta (skimmed milk cheese) = 90 mg
* brown sugar = 85 mg
* lentils = 79 mg
* wheat germ = 72 mg
* pigeon pea = 62.7 mg
* egg, 1 = 54 mg
* chickpea = 53.1
* flour = 41 mg
* orange = 40 mg
* human milk = 33 mg
* Rice, white, long-grain, parboiled, enriched, cooked = 19 mg
* trout = 19 mg
* beef = 12 mg
* cod = 11 mg
* horse meat = 10 mg
* honey = 5 mg
* white sugar = 0 mg

=References=

=External links=
* [http://www.nal.usda.gov/fnic/foodcomp/Data/SR17/wtrank/sr17a301.pdf USDA national nutritional database, Calcium content of selected foods]
* [http://www.nof.org/prevention/calcium.htm Calcium and vitamin D] .


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Calcium (disambiguation) — Calcium may refer to: * Calcium, the chemical element **Calcium 48, an isotope of calcium * Calcium in biology, the role that the calcium cation plays in biology * Calcium, New Yorkee also* * …   Wikipedia

  • Calcium — (pronEng|ˈkælsiəm) is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth s crust. Calcium is also …   Wikipedia

  • Calcium nitrate — Calcium nitrate …   Wikipedia

  • Calcium storage — Calcium (Ca2+ ) storages (in cell biology) are intracellular organelles, that constantly accumulate Ca2+ ions and release them during certain cellular events. Intracellular Ca2+ storages include mitochondria and the endoplasmic reticulum …   Wikipedia

  • Calcium lactate — Chembox new ImageFile=calcium lactate.png ImageSize=200px IUPACName=calcium 2 hydroxypropanoate OtherNames=calcium lactate 5 hydrate, calcium lactate, 2 hydroxypropanoic acid calcium salt pentahydrate Section1= Chembox Identifiers CASNo=814 80 2… …   Wikipedia

  • N-type calcium channel — Calcium channel, voltage dependent, N type, alpha 1B subunit Identifiers Symbols CACNA1B; BIII; CACNL1A5; CACNN; Cav2.2 External IDs …   Wikipedia

  • P-type calcium channel — calcium channel, voltage dependent, P/Q type, alpha 1A subunit Identifiers Symbol CACNA1A Alt. symbols Cav2.1, CACNL1A4, SCA6, MHP1, MHP IUPHAR Cav2.1 …   Wikipedia

  • Magnesium in biology — Magnesium is an essential element in biological systems. Magnesium occurs typically as the Mg2+ ion. It is an essential mineral nutrient for life[1][2][3] and is present in every cell type in every organism. For example, ATP (adenosine… …   Wikipedia

  • Voltage-dependent calcium channel — Voltage dependent calcium channels (VDCC) are a group of voltage gated ion channels found in excitable cells (e.g., muscle, glial cells, neurons, etc.) with a permeability to the ion Ca2+.[1][2] These channels are slightly permeable to sodium… …   Wikipedia

  • Egg (biology) — Bird eggs and others (click on image for key) …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.