Elemental composition of the dense bodies of rat platelets determined by electron probe x-ray microanalysis of freeze-substituted sections.

A semiquantitative x-ray microanalytical study was made of dense bodies in rat and human blood platelets prepared by freeze substitution. After the freeze substitution, electron dense bodies containing 5-hydroxytryptamine(5-HT) were well preserved. Electron probe x-ray microanalyses clearly defined species differences in the cations of dense bodies of rat and man. Direct calculation of elemental concentration ratios demonstrated a high level of Mg, with lesser amounts of K and Ca in rat, while there was a negligible level of Mg in man but a high amount of Ca. These results indicate that freeze-substitution is a suitable preparation for the study of diffusible electrolytes which may open the way to quantitative analysis using appropriate standards for analytical electron microscopy of resin sections.