Receptor for inositol 1,4,5-trisphosphate, a second messenger that mediates the release of intracellular calcium. This release is regulated by cAMP both dependently and independently of PKA (By similarity). Homotetramer (PubMed:12032348). Interacts with CABP1 (PubMed:12032348). Interacts with BOK; regulates ITPR2 expression (PubMed:23884412). Interacts with BCL2L10 (By similarity). Interacts with TRPC4 (PubMed:11163362). 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.