DIFFERENTIAL EXPRESSION OF TYPE-2 AND TYPE-3 INOSITOL 1,4,5-TRISPHOSPHATE RECEPTOR MESSENGER-RNAS IN VARIOUS MOUSE-TISSUES - IN-SITU HYBRIDIZATION STUDY

The inositol 1,4,5-trisphosphate receptor (IP(3)R) is an intracellular Ca2+ release channel responsible for mobilizing stored Ca2+. Three different receptor types have been molecularly cloned, and their genes have been classified into a family. The gene for the type 1 receptor (IP(3)R1) is predominantly expressed in cerebellar Purkinje neurons, but its gene product is localized widely in a variety of tissues; however, there is little information on what types of cells express the other two receptor types, type 2 and type 3 (IP(3)R2 and IP(3)R3, respectively). We studied the expression of the IP(3)R gene family in various mouse tissues by in situ hybridization histochemistry. Compared with IP(3)R1, the levels of expression of IP(3)R2 and IP(3)R3 mRNAs were low in all of the tissues tested. IP(3)R2 mRNA was localized in the intralobular duct cells of the submandibular gland, the urinary tubule cells of the kidney, the epithelial cells of epididymal ducts and the follicular granulosa cells of the ovary, while the IP(3)R3 mRNA was distributed in gastric cells, salivary and pancreatic acinar cells and the epithelium of the small intestine. All of these cells which express either IP(3)R2 or IP(3)R3 mRNA are known to have a secretory function in which IP3/Ca2+ signalling has been shown to be involved, and thus either IP(3)R2 or IP(3)R3 may be a prerequisite to secretion in these cells.