CONTRIBUTION OF ENERGY-FILTERING TEM TO THE DETECTION OF CALCIUM - APPLICATION TO MAST-CELLS

The ultrastructural distribution and quantification of calcium in mast cells prepared by anhydrous processing was investigated by energy-fil tering transmission electron microscopy (EFTEM) using a Zeiss 902 elec tron microscope. Optimal conditions for calcium detection were determi ned using inorganic (calcium phosphate) and organic (calcium-loaded ch elex beads) standards with known amounts of calcium. Electron energy-l oss spectroscopy (EELS) revealed calcium at the L2,3 edge and also at the M2,3 edge for all specimens examined. Comparison with X-ray microa nalysis confirmed the results obtained with EELS. Electron spectroscop ic imaging (ESI) was applied for mapping calcium both in standards and in cells and we showed that mast cell granules were the main site of calcium localization. Although, results have shown that a combination of analytical techniques is required to obtain reliable results.