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. Isoform 3 has neither inositol 1,4,5-trisphosphate binding activity nor calcium releasing activity. Homotetramer. Interacts with CABP1. Interacts with BOK; regulates ITPR2 expression. Interacts with BCL2L10 (By similarity). Interacts with TRPC4 (By similarity). Isoforms 1 and 3 are widely expressed. Isoform 2 is found in skeletal muscle and heart. 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. There is a 3-fold reduction in the number of pilocarpine-responsive sweat glands in knockout animals. The sweat glands of these animals show a significant reduction in Ca(2+) response following acetylcholine stimulation compared with those of wild-type animals. The Itpr2-null animals retained some residual sweat production, in contrast to the human phenotype of anhidrosis. This phenotypic discrepancy may be due to differences between humans and mice in the expression of the 3 ITPR isoforms, as well as to the different stimuli used to provoke sweat production in Itpr2-null animals. Belongs to the InsP3 receptor family.