Progress in electron microscopic diagnostics: semi‐quantitative determination of precipitable calcium in different cell types of the organ of Corti in the guinea‐pig

SUMMARY Potassium antimonate was used to precipitate calcium in the cochlea of the guinea‐pig. The distribution of the calcium antimonate precipitates was analysed by electron microscopy. The precipitate density was determined in different cell types in the organ of Corti by counting the number of calcium binding sites in a 10‐μm 2 area. The size of the precipitates varied considerably, and thus the relative amount of the precipitable calcium was estimated only semi‐quantitatively. As the prominent carbon signal is superimposed over the nearby small Ca 2+ ‐edge signals, the combined signal of the antimony M 4,5 ‐edge and the oxygen K‐edge of the calcium antimonate salt formed was chosen for the semi‐quantitative estimation. Images of the inelastically scattered electrons of the precipitates at Δ E = 570 eV were recorded by electron spectroscopic imaging. The area covered by the calcium precipitates within a given cell type was determined in different ultrathin sections of the same organ of Corti by an image processing system.