A HYDROPHILIC RESIN-EMBEDDING METHOD FOR LIGHT AND ELECTRON-MICROSCOPIC DETECTION OF TISSUE ANIONIC SITES WITH CATIONIC COLLOIDAL IRON - ASAPPLIED TO MOUSE PANETH CELLS

A cationic colloidal iron method was introduced for electron microscop ic detection of anionic sites in hydrophilic resin-embedded specimens, and the method was applied to Paneth cells of the mouse jejunum. Mous e jejunal blocks were embedded in hydrophilic acrylic resin (LR White) , cut into ultrathin sections, stained with the diluted cationic collo idal iron, and exposed to osmium vapor. The jejunal tissues, including the Paneth cells, embedded in hydrophilic resin were reactive to the fine cationic colloidal iron. At pH value 1.5, fine electron dense col loidal iron deposited along the rims of the secretory granules and the Golgi apparatus of the Paneth cell. Colloidal particles distributed o n the osmiophilic reticular structures in the rim and in dot-like fash ion lined the border between the granular core and rim. At pH value 4. 0, ribosomes reacted to cationic colloidal iron particles in addition to the granular rims and Golgi apparatus. At pH 7.0, even the cores of the secretory granules were stained. Semi-thin sections prepared from the LR White-embedded specimens and stained at pH 1.5 with the dilute d (1:3 in volume) cationic colloidal iron showed sufficient Prussian b lue reaction for light microscopy in the rims of Paneth granules and m ucus of goblet cells. This method is therefore useful for correlative light and electron microscopic detection of tissue anionic sites, incl uding sulfate, carboxyl and phosphate groups, at various pH values.