inositol145trifosfat

Inositol 1,4,5-trisphosphate, commonly known as IP3, is a soluble second messenger that plays a central role in intracellular calcium signaling. It is produced when phospholipase C hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) in the plasma membrane, generating IP3 and diacylglycerol (DAG). Activation of G protein-coupled receptors that couple to the Gq alpha subunit or certain receptor tyrosine kinases leads to PLC activation and IP3 formation.

IP3 diffuses through the cytosol and binds to IP3 receptors, ligand-gated calcium channels located on the membrane of the endoplasmic reticulum. Binding opens the channel, releasing Ca2+ from ER stores into the cytoplasm, increasing intracellular calcium concentration. This Ca2+ signal can activate various effectors, including calcium-dependent enzymes, pumps, ion channels, and, together with DAG, protein kinase C (PKC).

IP3 signaling is tightly regulated: cytosolic Ca2+ and IP3 receptor properties influence the amplitude and duration of Ca2+ release. Termination involves dephosphorylation and further metabolism of IP3 to inositol phosphates, as well as re-sequestration of Ca2+ into ER by SERCA pumps and extrusion across the plasma membrane.

IP3 receptors exist in several subtypes (IP3R1-3) encoded by Itpr1-3 genes, with tissue-specific expression patterns that influence cellular Ca2+ dynamics. The IP3/DAG signaling system interacts with other pathways and is implicated in diverse physiological processes, including muscle contraction, secretion, neurotransmission, metabolism, and gene expression. IP3 is also a widely used laboratory tool to elicit intracellular Ca2+ release in experimental studies.