Inositol trisphosphate (IP3) is a signaling molecule produced in cells when a specific receptor is activated, often by a hormone or neurotransmitter. It plays a crucial role in cellular communication by triggering the release of calcium ions from the endoplasmic reticulum, which is essential for various cellular processes, including muscle contraction and neurotransmitter release. IP3 is part of a larger signaling pathway that involves phospholipase C, which converts a membrane lipid called phosphatidylinositol 4,5-bisphosphate (PIP2) into IP3 and diacylglycerol (DAG). This pathway is vital for many physiological functions, including regulating metabolism, cell growth, and immune responses.