 Inositol trisphosphate receptor

An IP3 receptor is an intracellular ligand-gated ion channel, rather than the extracellular signal's cell-surface receptor. Its opening is regulated by both IP3 and cytosolic calcium: IP3 binding is not a command that fixes one constant release rate. Mammalian IP3 receptors have three subtypes, with possible mixed assemblies and splice variants; these need not have identical regulation or cellular roles. The 2010 authored account distinguishes established channel behavior from then-unresolved structural explanations.^[ref]