LOCALIZATION OF INOSITOL 1,4,5-TRISPHOSPHATE RECEPTORS IN THE RAT-KIDNEY

Inositol 1,4,5-trisphosphate (IP3) receptors (IP(3)Rs) serve as intrac ellular calcium release channels involved in signal transduction of va rious hormones in the kidney. Molecular cloning studies have shown tha t there are three types of IP3R, designated type 1, type 2, and type 3 . To characterize their localizations in the rat kidney, we employed i mmunohistochemical studies using type-specific monoclonal antibodies t hat were raised against the 15 C-terminal amino acids of each type of IP3R. Type 1 was detected in glomerular mesangial cells and vascular s mooth muscle cells. Type 2 was expressed exclusively in intercalated c ells of collecting duels from the cortex to the inner medulla. Type 3 was expressed in vascular smooth muscle cells, glomerular mesangial ce lls, and some cells of cortical collecting ducts, probably principal c ells. As to the subcellular distribution, type 1 and type 2 showed a h omogenous distribution in the cytoplasm, whereas type 3 was present ma inly in the basolateral portion of the cytoplasm. These results indica te that IP3R isoforms were expressed in a cell-specific manner. The he terogeneous subcellular localizations among the IP3R types suggests co mpartmentalization of distinct IP3-sensitive Ca2+ pools.