Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP or Ins3P or IP is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP), a phospholipid that is located in the plasma membrane, by phospholipase C (PLC).
Together with diacylglycerol (DAG), IP is a second messenger molecule used in signal transduction in biological cells. While DAG stays inside the membrane, IP is soluble and diffuses through the cell, where it binds to its receptor, which is a calcium channel located in the endoplasmic reticulum. When IP binds its receptor, calcium is released into the cytosol, thereby activating various calcium regulated intracellular signals.