IMMUNOHISTOCHEMICAL LOCALIZATION OF INOSITOL 1,4,5-TRISPHOSPHATE RECEPTORS IN NONNEURAL TISSUES, WITH SPECIAL REFERENCE TO EPITHELIA, THE REPRODUCTIVE-SYSTEM, AND MUSCULAR TISSUES

Although the pharmacological properties and distribution of inositol 1 ,4,5-trisphosphate (IP3)-sensitive calcium stores vary considerably am ong tissues, studies of its localization have been devoted mostly to t he central nervous system. In this report we have analyzed the localiz ation of IP3 receptors in diverse non-neural tissues of the mouse, usi ng polyclonal antibodies raised against purified IP3 receptors through immunoblotting and immunohistochemistry. These antibodies mainly reco gnized type 1 IP3 receptors, although they also reacted with other typ es of IP3 receptors. The receptors were localized in the apical surfac e areas of highly polarized epithelia, such as the choroid plexus, ret inal pigment epithelium, and columnar epithelium lining the interlobul ar ducts in the sublingual and submaxillary salivary glands. Immunoele ctron microscopy of choroidal cells revealed that IF3 receptors are lo calized on the surfaces of several structures, including clear vesicle s, tubules and vesicular profiles of smooth endoplasmic reticulum, rou gh endoplasmic reticulum and a part of the nuclear envelope; as well a s clusters of ribosomes in the cytoplasmic matrix. The surface areas o f ciliated epithelia, such as those of the trachea and oviduct, also s tained positive. The cytoplasmic distribution was homogeneous in mesan gial cells, myoepithelial cells, and endothelial cells accompanying mu scle, as well as in a population of endocrine cells. Intense immunosta ining was found in the surface areas as well as in the cytoplasm of di verse smooth muscle cells. Staining intensity of smooth muscle varied among cells in the same tissue. Staining was intense in the cytoplasm of premature oocytes in the primary follicle, but then attenuated as t hese cells matured. The Sertoli cells with clusters of elongating matu ring sperm were stained, but mature sperm were unstained. These result s indicate a heterogeneous cellular distribution, and possibly a heter ogeneous subcellular distribution, of a population of IF3 receptors in a variety of non-neural tissues.