Inositol 1,4,5,-tris-phosphate receptor
The Inositol 1,4,5,-trisphosphate receptor, often abbreviated to 'InsP3R' or 'IP3R' is a key integral membrane protein ion channel responsible for the release of Ca2+ ions from both the Endoplasmic and Sarcoplasmic Reticulum, into the cell cytosol. As the name suggests, it is triggered by the binding of IP3 (Inositol 1,4,5,-tris-phosphate), in the presence of Ca2+.
In order for the channel to open, ATP must be present at the ATP binding site. Note, the ATP is not hydrolised as an energy source by the IP3R, it merely requires ATP as a binding ligand for activation.
IP3R is a key protein in many fundamental biological processes such as cell death, insulin regulation and platelet activation, to name a few . It is fundamental in generating global Ca2+ waves via Calcium Induced Calcium Release (CICR), as well as elemental (puffs) and fundamental calcium signals.