Inositol triphosphate receptor (IP3R) is a membrane glycoprotein complex acting as Ca2+ channel activated by inositol triphosphate (IP3).
It has a broad tissue distribution but is especially abundant in the cerebellum. Most of the IP3R's are found in the cell integrated into the endoplasmic reticulum.
The IP3R complex is formed of four 313 kDa subunits. In amphibians, fish and mammals there are 3 paralogs and these can form homo- or hetero-oligomers. IP3R-1 is the most widely expressed of these three and is found in all tissue types and all developmental stages of life. It is additionally the means for further IP3 receptor diversity in that it has as many as four splice sites with as many as 9 different optional exons or exon variants. Combinations of these can be introduced into a given transcript in order to modulate its pharmacological activity.