Optimal freeze-drying of cryosections and bulk specimens for X-ray microanalysis

Electron microscopic investigations of rapidly frozen specimens of striated muscle, either frozen-hydrated or obtained after different dehydration procedures, have shown that the subcellular distribution of the main cellular cation K+ or its surrogates Rb+, Cs+, or Tl+ does not follow the water distribution but follows certain proteins. Conflicting results obtained by X-ray microanalysis of freeze-dried cryosections are explained by showing that freeze-drying of bulk specimens and cryosections must be carried out for rather long periods at low temperature in order to avoid severe shrinkage and ion redistribution artefacts. Proposals for future freeze-drying studies are derived from the concept that cellular water is organized differently from normal free water and that proteins of living cells are able to selectively adsorb alkali-metal ions.