Ions and Water in Cells and Tissues Studied by Microprobe Analysis of Frozen-Hydrated Sections in the SEM

Electrolyte elements including Na, K, Cl, Ca and Mg are increasingly implicated in a variety of cell and tissue functions. A proper understanding of their role requires knowledge of the distribution of these elements in and around cells at microscopic levels. There has been a lack of suitable methods to measure elemental concentrations in microvolumes in situ. The electron probe x-ray microanalysis (microprobe analysis) of frozen sections is proving effective in providing such data. The total concentrations in subcompartments measured by microprobe analysis can be compared with the free concentrations and the activities measured by other methods such as microelectrodes to yield information on the possible binding or sequestration sites for the elements concerned. Method. The technique of microprobe analysis of thick(>0.5 μm) frozen-hydrated sections in a scanning electron microscope column (SEM) was initiated and developed and has been applied in our laboratory to investigate a range of cellular transport processes.