Metabolic state dependent preservation of cells by fixatives for electron microscopy

The preservation of mitochondria, cytoplasmic vacuoles and cytoplasm by various fixatives after various pretreatments of ethothelial heart cells from Xenopus laevis tadpoles in tissue culture was investigated. The study was based on phase contrast cinemicrographic recordings and on qualitative and quantitative observations with the electron microscope. Three fixatives were used: 3% glutaraldehyde in phosphate buffer, followed by 1% osmium tetroxide postfixation, fixation only with 1% osmium tetroxide in phosphate buffer and the fixing medium according to Dalton. Cells were either not treated or pretreated for 20 min: 10 microM FCCP (Carbonylcyanide-p-trifluoromethoxy-phenylhydrazone) or 4 mM KCN. The superiority of glutaraldehyde was exemplified by its very rapid action, good preservation of cytoplasm, vacuoles, and mitochondria. It was the only medium which maintained an electron density of the mithochondria matrix. In both of the other fixatives swelling of mitochondria and coagulated appearance of cytoplasm (in phase contrast) was more pronounced in cells pretreated with metabolic inhibitors than in controls. Observations with the light microscope have been confirmed by morphometry of electron micrographs of mitochondria. The relation of matrix space to intracristal space is changed in opposite directions after glutaraldehyde and after the Dalton-type fixation. The results indicate a higher sensitivity against fixation artifacts in cells under pathological conditions than normal cells.