Editing Inositol trisphosphate (section)

==Function==

===Human===
{{see also|Functions of calcium in humans}}
IP<sub>3</sub>'s main functions are to mobilize Ca<sup>2+</sup> from storage [[organelle]]s and to regulate [[cell proliferation]] and other cellular reactions that require free calcium. In [[smooth muscle cell]]s, for example, an increase in concentration of cytoplasmic Ca<sup>2+</sup> results in the contraction of the muscle cell.<ref>{{cite journal |last1= Somlyo |first1= AP |last2= Somlyo |first2= AV |title= Signal transduction and regulation in smooth muscle |journal= [[Nature (journal)|Nature]] |volume= 372 |issue= 6503 |pages= 231–6 |year= 1994 |pmid= 7969467 |doi= 10.1038/372231a0|bibcode= 1994Natur.372..231S |s2cid= 4362367 }}</ref>

In the nervous system, IP<sub>3</sub> serves as a second messenger, with the [[cerebellum]] containing the highest concentration of IP<sub>3</sub> receptors.<ref>{{cite journal |last1= Worley |first1= PF |last2= Baraban |first2= JM |last3= Snyder |first3= SH |title= Inositol 1,4,5-trisphosphate receptor binding: autoradiographic localization in rat brain |journal= [[J. Neurosci.]] |volume= 9 |issue= 1 |pages= 339–46 |year= 1989 |pmid= 2536419|doi= 10.1523/JNEUROSCI.09-01-00339.1989 |pmc= 6569993 }}</ref> There is evidence that IP<sub>3</sub> receptors play an important role in the induction of plasticity in cerebellar [[Purkinje cells]].<ref>{{cite journal |last1= Sarkisov |first1= DV |last2= Wang |first2= SS |title= Order-dependent coincidence detection in cerebellar Purkinje neurons at the inositol trisphosphate receptor |journal= [[J. Neurosci.]] |volume= 28 |issue= 1 |pages= 133–42 |year= 2008 |pmid= 18171931 |doi= 10.1523/JNEUROSCI.1729-07.2008|pmc= 6671165 |doi-access= free }}</ref>

=== Sea urchin eggs ===
The [[Egg activation#Fast and slow block to polyspermy|slow block to polyspermy]] in the [[sea urchin]] is mediated by the PIP<sub>2</sub> secondary messenger system. Activation of the binding receptors activates PLC, which cleaves PIP<sub>2</sub> in the egg plasma membrane, releasing IP<sub>3</sub> into the egg cell cytoplasm. IP<sub>3</sub> diffuses to the ER, where it opens Ca<sup>2+</sup> channels.