Receptor for inositol 1,4,5-trisphosphate, a second messenger that regulates intracellular calcium homeostasis (PubMed:10499793, PubMed:10610772, PubMed:15194811, PubMed:16186564, PubMed:23671426). Binds in vitro to both inositol 1,4,5-trisphosphate (1,4,5-InsP3) and inositol 2,4,5-trisphosphate (2,4,5-InsP3) with high affinity and does not discriminate between the phosphate at 1 or 2 position (PubMed:10610772). Can also bind inositol 1,3,4,5-tetrakisphosphate (1,3,4,5-InsP4) and inositol 4,5-bisphosphate (4,5-InsP2), but with lower affinity (PubMed:10610772). Acts as a timekeeper/rhythm generator via calcium signaling, affecting the defecation cycle and pharyngeal pumping (PubMed:10499793, PubMed:11553721, PubMed:12062062, PubMed:11950942, PubMed:15013747, PubMed:15133127, PubMed:16186564, PubMed:21191812). Affects normal hermaphrodite and male fertility as a participant in intracellular signaling by acting downstream of let-23/lin-3 which regulates ovulation, spermathecal valve dilation and male mating behavior (PubMed:9491893, PubMed:15194811, PubMed:16267094, PubMed:15958491). Important for early embryonic development; controls epidermal cell migration and may also regulate filopodial protrusive activity during epithelial morphogenesis (PubMed:11950942, PubMed:15498499, PubMed:18369461). Component of inositol trisphosphate (IP3)-mediated downstream signaling pathways that controls amphid sensory neuronal (ASH)-mediated response to nose touch and benzaldehyde but not other ASH-mediated responses (PubMed:19730689). Involved in modulating lifespan, acting downstream of transcription factor atf-6 (PubMed:32905769). Interacts with myo-1, myo-2, unc-54/myo-4 and nmy-2. Also interacts with iri-1. Isoform a is expressed in the anterior cells of the pharyngeal terminal bulb, vulva, rectal epithelial cells, spicule protractor muscles of the proctodeum and male-specific neuron CP8 or CP9. Isoform d is expressed in the spermatheca, excretory cell, amphid socket cells, PDA motor neuron, spicule retractor muscles, gubernaculum retractor muscles, posterior oblique muscles, diagonal muscles and the vas deferens. Also expressed in the intestine, pharynx, pharyngeal isthmus, pharyngeal intestinal valve, somatic gonad, hypodermal cells of the vulva, uterine sheath cells, tail, head, LUA motor neuron and the embryonic epidermis (at protein level). 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. Disrupted defecation rhythm with reduced pharyngeal pumping in the presence of food resulting in constipation. Disrupted reversal/avoidance response to nose touch. Hermaphrodites display endomitotic oocytes following spermathecal dilation defect and defective ovulation. Loss of male fertility due to defects in turning behavior, spicule insertion and sperm transfer. Produced by alternative promoter usage. Produced by alternative promoter usage. Produced by alternative promoter usage and alternative splicing. Produced by alternative promoter usage and alternative splicing. Produced by alternative promoter usage and alternative splicing. Produced by alternative promoter usage and alternative splicing. Belongs to the InsP3 receptor family.