Inositol 1,4,5 trisphosphate

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A small molecule, often abbreviated IP3, involved in intracellular signalling. It is produced when the inositol phospholipid signalling pathway is activated and is one of the main factors in the release of Ca2+ ions from the endoplasmic reticulum [1].

Inositol 1,4,5-trisphosphate (IP3) is a common secondary messenger used in signal transduction. When phosphatidylinositol 4,5-bisphosphate (PIP2) is hydrolysed by phospholipase C it produces IP3 and diacylglycerol (DAG) [2].  IP3 is soluble so can diffuse through the cell to its IP3 receptor (InsP3R) on the endoplasmic reticulum or sarcoplasmic reticulum. IP3 receptor acts as a calcium ion channel, so once IP3 is bound it allows the movement of Ca2+ ions from the endoplasmic reticulum into the cell down their concentration gradient. This influx of calcium causes a calcium induced calcium response (CICR) which along with IP3 helps to activate many more InsP3R [3],  leading to a huge amplification of Ca2+ in the cell.

IP3 (Inositol 1,4,5-trisphosphate) is a cleavage product of phosphatidylinositol 4,5-bisphosphate (PIP2). PIP2 is a phospholipid molecule cleaved into inositol 1,4,5-trisphosphate and diacylglycerol (DAG) by phospholipase C after hormone binding to the receptor. Inositol 1,4,5-trisphosphate binds to IP3receptor which results to the release of calcium from the calcium pumps

Also see cell and membrane transport


  1. Alberts B., Johnson A., Lewis J., Raff M., Roberts K., Walter P., (2008), Molecular Biology of the Cell, 5th Edition, New York: Garland Science
  2. Alberts et al, 2008, Mollecular biology of the Cell, 5th edition, New York, Garland publishing
  3. C.H.Heldin & M Purton, 1996, Signal transduction, Chapman & Hall
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