Receptor for inositol 1,4,5-trisphosphate, a second messenger that mediates the release of intracellular calcium (PubMed:11584008). This release is regulated by cAMP both dependently and independently of PKA (By similarity). Homotetramer. Interacts with CABP1. Interacts with BOK; regulates ITPR2 expression. Interacts with BCL2L10 (By similarity). Interacts with TRPC4 (By similarity). Endoplasmic reticulum and secretory granules. The receptor contains a calcium channel in its C-terminal extremity. Its large N-terminal cytoplasmic region has the ligand-binding site in the N-terminus and modulatory sites in the middle portion immediately upstream of the channel region. Phosphorylation by cAMP-dependent PKA on Ser-937 increases calcium release. Belongs to the InsP3 receptor family.