InsP3

Inositol trisphosphate, often abbreviated as InsP3 or IP3, is a crucial second messenger molecule in eukaryotic signal transduction pathways. It is a water-soluble inositol phosphate derived from the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid found in the cell membrane. This hydrolysis is typically catalyzed by the enzyme phospholipase C (PLC).

Upon its formation within the cell, InsP3 plays a pivotal role in mobilizing intracellular calcium stores. It diffuses through the cytoplasm and binds to specific receptors, known as InsP3 receptors (IP3Rs), which are primarily located on the endoplasmic reticulum. The binding of InsP3 to these receptors causes a conformational change, leading to the opening of calcium channels embedded in the ER membrane. This allows stored calcium ions to be released into the cytosol, significantly increasing the intracellular calcium concentration.

The rise in cytosolic calcium acts as a signal for a wide array of cellular processes. These include muscle contraction, neurotransmitter release, gene expression, cell motility, and programmed cell death (apoptosis). The tightly regulated release of calcium mediated by InsP3 and its receptors is fundamental to numerous physiological functions across diverse cell types. The concentration of InsP3 is dynamically regulated by its synthesis and degradation, ensuring precise control over calcium signaling.