Quantitative X-ray microanalysis of calcium in sea urchin eggs after quick-freezing and freeze-substitution |
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Authors: | I. Gillot B. Ciapa P. Payan G. De Renzis G. Nicaise C. Sardet |
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Affiliation: | (1) Station Zoologique, Unité de Biologie Cellulaire Marine URA 671 CNRS/Paris VI, F-06230 Villefranche-sur-mer, France;(2) Laboratoire de Physiologie Cellulaire et Comparée, CNRS URA 651, Université de Nice, Parc Valrose, F-06034 Nice Cedex, France;(3) Laboratoire de Cytologie Expérimentale, CNRS URA 651, Université de Nice, Parc Valrose, F-06034 Nice Cedex, France |
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Abstract: | Summary Freeze-substitution was used to study the distribution of calcium in sea urchin eggs, and the validity of the technique was assessed. We followed the fate of both total and exchangeable calcium of sea urchin eggs in two species (Paracentrotus lividus and Arbacia lixula) after the various treatments needed for freeze-substitution and embedding. We compared the calcium content either by X-ray microanalysis of Epon-embedded sections of freeze-substituted eggs (6.2±0.71 mmoles/kg of Epon-embedded tissue) or by flame spectrometry analysis of living eggs (32.3±1.30 nmoles/mg protein). After standardization of units, both values lead to similar total calcium content. We also measured the movements of 45Ca from prelabelled eggs. Exchangeable 45Ca as well as total calcium appeared unaffected by the preparative treatment for X-ray microanalysis. In conclusion, our preparative technique for X-ray microanalysis can be considered appropriate for our material and allows us to undertake a subcellular quantification of calcium in various organelles. |
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