Elemental composition of pyroantimonate precipitates analysed by electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS) in vitellogenic ovarian follicles of Drosophila

Cytochemical localization of calcium in prefusion myoblasts from the chick embryo myotome

Myoblast fusion is a Ca2+-dependent process. The aim of this report was to study the localization of Ca2+ in prefusion myoblasts from the brachial somites of chick embryos (51-108 h of incubation), using the potassium pyroantimonate cytochemical method. When observed under a transmission electron microscope, electron-dense precipitates of Ca2+-antimonate were found in the basement membrane of the myotome, which separates the myotome from the adjacent mesenchyma. Within myoblasts, triads and sarcoplasmic reticulum associated with the first newly formed sarcomeres were observed, but a T-tubule network was not found. Moreover, Ca2+-antimonate precipitates were not observed in structures resembling T-tubules or sarcoplasmic reticulum. The results suggest that sarcomerogenesis and sarcoplasmic reticulum development occur simultaneously and that prefusion myoblasts have neither a T-tubule network nor Ca2+ deposits on sarcoplasmic reticulum. Small Ca2+ pools were found in the myoblast nuclei, cytoplasmic vesicles and mitochondrias. Ca2+-antimonate precipitates periodically distributed at the cell periphery, close to the cell membrane, were observed. These precipitates could represent internal Ca2+ stores located in the peripheral couplings and it is proposed that these pools of Ca2+ could be mobilized before fusion, leading to the increase in free intracellular Ca2+ that precedes myoblast fusion.

Localisation of potassium pumps in Drosophila ovarian follicles

It has been shown previously that, in Drosophila oogenesis, potassium ions are important for bioelectric phenomena as well as for other physiological and developmental processes. In the present study we determined the spatial distribution and activity of the Na+,K+)-pump and of ouabain-insensitive K+ pumps in plasma membranes of vitellogenic ovarian follicles (stage 10). We used the light microscopic anthroylouabain method as well as the cytochemical lead and cerium precipitation methods in combination with electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS). (Na+,K+)-ATPase activity was predominantly observed on the oolemma as well as on the membranes of the columnar follicle cells covering the oocyte, whereas on the membranes of the nurse cells and of the squamous follicle cells covering the nurse cells the activity was very low. The highest activity of the (Na+,K+)-pump was found at the anterior and posterior ends of the oocyte, and this on the oolemma as well as on the membranes of the follicle cells located here. Strong activity of the ouabain-insensitive K+-pumps was observed on most of the oolemma (except at the anterior of the oocyte) and on the membranes of some nurse cells located next to the oocyte, whereas less activity was found on the other nurse cell membranes and on the membranes of all follicle cells. The suitability of the different methods used for determining the localisation as well as the activity of K+-pumps is discussed. We further discuss the nature of the ouabain-insensitive K+ pumps and the relevance of the observed distribution of K+-pumps for K+ uptake, extrafollicular ionic current flow, intercellular signalling and other developmental processes in Drosophila oogenesis.

Differences of inner and outer hair cells in the organ of Corti of the guinea pig in respect to the cellular content of precipitable calcium

Differences between inner and outer hair cells in the cellular content of precipitable calcium were detected using a potassium pyroantimonate precipitation method and the electron spectroscopic imaging (ESI-) technique. The cytoplasm of the inner hair cells was scattered with a high number of calcium precipitates in all analysed animals, but only a few reaction products could be identified in the cytoplasm of the outer hair cells in all analyzed specimens. Even the well developed system of the subsurface fenestrated cisternae in the outer hair cells was nearly empty of calcium precipitates. A relatively high amount of reaction products could be identified in the nuclei of both types of nerve endings of the receptor cells. Significant differences regarding the content of precipitable calcium were found in the different types of nerve endings, which come into contact with the basal parts of both receptor cells. The observed differences in the content of precipitable calcium between the two types of hair cells are discussed with respect to their probable different roles in signal transduction processes.

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.

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

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-micron 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 M4,5-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 delta 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.