Enables inositol 1,4,5-trisphosphate receptor activity involved in regulation of postsynaptic cytosolic calcium levels; phosphatidylinositol binding activity; and protein domain specific binding activity. Involved in several processes, including epithelial fluid transport; intrinsic apoptotic signaling pathway in response to endoplasmic reticulum stress; and release of sequestered calcium ion into cytosol. Acts upstream of or within several processes, including calcium ion transport; endoplasmic reticulum calcium ion homeostasis; and voluntary musculoskeletal movement. Located in endoplasmic reticulum; nucleus; and postsynaptic density. Part of calcineurin complex. Is active in Schaffer collateral - CA1 synapse. Is expressed in several structures, including brain; brown fat; genitourinary system; heart; and hemolymphoid system. Human ortholog(s) of this gene implicated in Gillespie syndrome; spinocerebellar ataxia type 15; and spinocerebellar ataxia type 29. Orthologous to human ITPR1 (inositol 1,4,5-trisphosphate receptor type 1). [provided by Alliance of Genome Resources, Apr 2022]