Immunohistochemical localisation of two phosphatidylinositol 4-kinase isoforms, P14K230 and P14K92, in the central nervous system of rats

The distribution and cellular localisation of the phosphatidylinositol 4-ki nase isoforms, PI4K230 and PI4K92, that are believed to play important role s in the intracellular signalling mechanisms were studied in the rat brain (cortex, cerebellum, hippocampus and spinal cord) using immunocytochemistry with light and electron microscopy. PI4K230 was detected with a specific a ntibody purified by affinity chromatography from the egg yolk of chicken im munised with a 33-kDa fragment of bovine PI4K230, comprising amino acids 87 3-1175 of the native protein. PI4K92 was immunostained with a commercially available antibody raised in rabbit against amino acid residues 410-537 of human PI4K92. At the light microscopic level, the immunostaining of PI4K230 and PI4K92 showed a very similar distribution throughout the neurons and a ppeared as dense punctate labelling in the cytoplasm of perikarya and stem dendrites of various neurons. In addition to neurons, a strongly stained ce ll population was observed in the molecular layer of the cerebellar cortex that resembled Bergmann glia cells. Electron microscopy of neurons in the v entral horn of the spinal cord showed dense granular immunoprecipitates for both PI4K230 and PI4K92, mostly associated with the outer membrane of mito chondria and membranes of the rough endoplasmic reticulum. In addition, imm unostaining of PI4K92 was also frequently found on the outer surface of cis terns and vesicles of Golgi complexes, whereas PI4K230 immunoreactivity was colocalised with some multivesicular bodies. Neither nuclear localisation nor a regular attachment to the cell membrane of these enzymes were observe d. Our findings indicate that PI4K230 and PI4K92 are not involved directly in the ligand-stimulated turnover of phosphoinositides at the plasma membra ne of neurons. However, they may provide regulatory phosphoinositides for i ntracellular vesicular traffic being associated with various organelles.