Receptor for inositol 1,4,5-trisphosphate, a second messenger that mediates the release of intracellular calcium (PubMed:1322910). Together with MCU, has a role in oxidative stress-induced ER-mitochondria calcium transfer (PubMed:28726639). May be involved in visual and olfactory transduction, and myoblast proliferation (PubMed:1322910). May be involved in ethanol tolerance (PubMed:29444420). Homotetramer. Segmental expression of isoform B is first detected in stage 13 embryos in lateral and posterior epidermis. Expression extends to head region during stages 13-17: gnathal buds, clypeolabrum, procephalic lobe, labial organ and anterior sense organs. Adults exhibit high expression in antenna and lower expression in retina, head, legs and thorax. Isoform A is expressed only in early embryos. Isoform B is expressed from mid-late embryos to adults. Predominant expression is in the adult. 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. RNAi-mediated knockdown in the perineurial glia results in decreased ethanol tolerance following repeated ethanol exposure (PubMed:29444420). RNAi-mediated knockdown in muscle reduces mitochondrial calcium uptake (PubMed:28726639). Belongs to the InsP3 receptor family.