Localization of Ca(2+)-stores and tissue compartments with a Ca(2+)-binding capacity in the organ of Corti of the guinea-pig by electron energy-loss spectroscopy.

The addition of 10 mM CaCl2 to glutaraldehyde fixative leads to the formation of small electron-dense deposits in the organ of Corti of the guinea-pig. These precipitates are mainly attached to cell membranes in contact with different extracellular lymphatic fluids. A higher number of precipitates is localized in the acellular parts of tectorial and basilar membrane. Electron energy-loss spectroscopy (EELS) was used to determine the elemental composition of the deposits formed. The spectra showed a prominent signal at the Ca2+ L2,3 ionization edge. Oxygen could also be detected in all the precipitates analysed. EELS analysis of mitochondria of the inner and outer hair cells after conventional fixation (glutaraldehyde followed by post-fixation in OsO4) revealed a small but significant calcium signal.