- Calcium signaling
Calcium can act in
signal transduction after influx resulting from activation ofion channels or as a second messenger caused by indirect signal transduction pathways such asG protein-coupled receptors . Calcium is a common signaling mechanism, as once it enters the cytoplasm it exerts allosteric regulatory affects on many enzymes and proteins.Calcium signaling through ion channels
Movement of calcium ions from the extracellular compartment to the intracellular compartment alters membrane depolarisation. This is seen in the heart, during the plateau phase of ventricular contraction. In this example, calcium acts to maintain depolarisation of the heart.
Calcium as a secondary messenger
Important physiological roles for calcium signaling include
muscle contraction , and cellularmotility , including the movement offlagella andcilia . Other biochemical roles of calcium include regulatingenzyme activity, ion pumps, and components of thecytoskeleton . [Koolman, Roehm. "Color Atlas of Biochemistry". Thieme, 2005 ISBN 1-58890-247-1]Signaling occurs when the cell is stimulated to release calcium ions (Ca2+) from intracellular stores. The resting concentration of Ca2+ in the
cytoplasm is normally maintained in the range of 10 - 100 nM. To maintain this low concentration, Ca2+ is actively pumped from the cytosol and accumulated in theendoplasmic reticulum (ER), and sometimes in themitochondria . Certain proteins of the cytoplasm and organelles act as buffers by binding Ca2+.Specific signals can trigger a sudden increase in the cytoplasmic Ca2+ level up to 500 - 1 000 nM by opening channels in the
endoplasmic reticulum or theplasma membrane . Many of Ca2+-mediated events occur when the released Ca2+ binds to and activates the regulatory proteincalmodulin .After cytoplasmic calcium has been depleted, Ca2+ can be imported from outside the cell by activation of "Store Operated Channels" (SOCs). This inflowing calcium current that results after stored calcium reserves have been released is referred to as Ca2+-release-activated Ca2+ current (
ICRAC ). The mechanisms through which ICRAC occurs are currently still under investigation, although two candidate molecules, Orai1 andSTIM1 have been linked by several studies, and a model of store-operatedcalcium influx , involving these molecules, has been proposed. Recent studies have cited thephospholipase A2 beta, [Csutora P, Zarayskiy V, Peter K, Monje F, Smani T, Zakharov S, Litvinov D, Bolotina VM (2006) "J Biol Chem" 281 :34926-34945.] nicotinic acid adenine dinucleotide phosphate (NAADP), [Moccia F, Lim D, Nusco GA, Ercolano E, Santella L (2003) "FASEB" J 17: 1907-1909] and the protein STIM 1 [Baba Y, et al. (2006) "Proc Natl Acad Sci USA" 103:16704-9] as possible mediators of ICRAC.History
*cite journal
quotes = yes
last=Petersen
first=Ole H
authorlink=
year=2005
month=
title=Ca2+ signalling and Ca2+-activated ion channels in exocrine acinar cells
journal=Cell Calcium
volume=38
issue=3-4
pages=171–200
publisher = | location = | issn =
pmid = 16107275
doi = 10.1016/j.ceca.2005.06.024
bibcode = | oclc =| id = | url = | language = | format = | accessdate = | laysummary = | laysource = | laydate = | quote =References
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