Receptor for inositol 1,4,5-trisphosphate, a second messenger that mediates the release of intracellular calcium. Homotetramer. Interacts with TRPC1, TRPC3 and TRPC4. Interacts with TRPV4 (PubMed:18826956). Interacts with SIGMAR1 (By similarity). Interacts with PML and AKT1 (By similarity). Interacts with IRAG2 (via coiled-coil domain) (By similarity). Interacts with CABP1 (PubMed:12032348). Interacts with TMBIM4/LFG4 (PubMed:19553469). Interacts with CEMIP (PubMed:23936024). Interacts with TESPA1 (By similarity). Interacts with TMEM203 (PubMed:25996873). Interacts with BOK; regulates ITPR3 expression (By similarity). Interacts with BCL2L10 (PubMed:27995898). Expressed in intestinal crypt and villus epithelial cells. 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. Phosphorylated on tyrosine residues. Phosphorylated by AKT1 on serine and/or threonine residues (By similarity). Belongs to the InsP3 receptor family.