Inositol trisphosphate or inositol 1,4,5-trisphosphate (also commonly known as triphosphoinositol; abbreviated InsP3 or IP3), together with diacylglycerol, is a second messenger molecule used in signal transduction in biological cells. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, by phospholipase C.
IP3 binds to and activates the InsP3 receptor on the membrane of the sarcoplasmic reticulum (SR) opens a calcium channel, resulting in the release of Ca2+ into the sarcoplasm. This increase in Ca2+ activates the ryanodine receptor-operated channel on the SR, leading to a further increase in the Ca2+.
In smooth muscle cells, for example, the increase in calcium concentration cell results in contraction of the muscle cell.. For further reading of Ca2+-mediated functions, see functions of calcium in humans.
- inositol phosphate
- inositol pentakisphosphate
- inositol hexaphosphate
- inositol triphosphate receptor
- Ferris CD, Snyder SH. IP3 receptors. Ligand-activated calcium channels in multiple forms. Adv Second Messenger Phosphoprotein Res. 1992;26:95-107. PMID 1329896
- Somlyo AP, Somlyo AV. Signal transduction and regulation in smooth muscle. Nature. 1994 Nov 17;372(6503):231-6. PMID 7969467