Inositol 1,4,5 trisphosphate
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) [1]. 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 [2], leading to a huge amplification of Ca2+ in the cell.