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 (By similarity). Interacts with SIGMAR1 (By similarity). Interacts with PML and AKT1 (By similarity). Interacts with IRAG2 (via coiled-coil domain) (By similarity). Interacts with CABP1. Interacts with TMBIM4/LFG4. Interacts with CEMIP (By similarity). Interacts with TESPA1 (By similarity). Interacts with TMEM203 (By similarity). Interacts with BOK; regulates ITPR3 expression (By similarity). Interacts with BCL2L10. 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. Phosphorylated on tyrosine residues. Phosphorylated by AKT1 on serine and/or threonine residues (By similarity). Belongs to the InsP3 receptor family.