Diffusible Ion Localization in Biological Tissue by Ion Microscopy

Abstract

The ion microscope is a particularly sensitive analytical tool for the localization of ions such as sodium, potassium and calcium which are highly diffusible and of considerable interest in many biological systems. Histochemical information obtained from ion micrographs of samples processed by conventional methods of tissue preparation (chemical fixation, dehydration, embedding in plastic and thin sectioning) agrees well, in many cases, with microanalysis reported using other methods. However, the possibility of ion loss and redistribution introduced by the preparation method introduces some question as to the validity of ion distribution observed for ions not strongly bound to the biological matrix.

The necessity of low temperature preparative procedures for diffusible ion localization at the 1 μm level, which is the spatial resolution of the CAMECA IMS-300 direct imaging ion microanalyzer, will be discussed. Methods of cryo-fixation, low temperature sectioning and freeze-drying will be presented with a discussion of their effect on the resulting ion image. Application of cryotechniques to specific biological systems in pathology, pharmacology and botany will also be discussed.