On the occurence and composition of dense particles in mitochondria in ultrathin frozen dry sections

Mitochondrial matrix granules: their behavior during changing metabolic situations and their relationship to contact sites between inner and outer mitochondrial membranes

Since their discovery in the early fifties mitochondrial granules have been the subject of many researches. Some twenty years ago two hypotheses on their function were introduced. Peachey thought that the granules were a sink of cations and that they would eventually regulate the concentrations of these ions. Alternatively, Barnard thought that the granules were precursors of the mitochondrial inner membrane. There are only a few data on organic constituents of the granules. Phospholipids (e.g., cardiolipin) glycoprotein or lipids, calcium precipitable lipoprotein, cytochrome c oxidase seem to be present in the granules. There has been much debate on whether calcium is present or not. Reports are mostly based on X-ray microanalysis, the result of which depends on preparation techniques. In heart muscle in stimulating situations the NMG (native matrix granules) move towards the inner membrane and are incorporated in it. They appear to create contact sites between inner and outer mitochondrial membranes in which enzymes can function efficiently. It is hypothetized that the system, NMG-contact sites, forms the structural basis of a regulatory mechanism, by which cells can cope with a high and sudden energy demand.

A study of calcification in the leg tendons from the domestic turkey

Details are presented of the structure and the spatial and temporal sequence of calcification within leg tendons obtained from the domestic turkey, Meleagris gallopavo. Histological and ultrastructural examination of the tissues reveals the development of large tendonoblasts, disposed in columns parallel to tendon long axes. Maturing cells are characterized by organelles active in protein synthesis, few mitochondrial granules, and an extensive system of processes. Deposition of mineral in the extracellular tissue spaces appears initially associated with small vesicular structures located between collagen fibrils. As calcification progresses, mineral is associated predominantly with collagen. Electron diffraction and electron probe microanalysis indicate that the mineral is a poorly crystalline hydroxyapatite having a Ca/P molar ratio ranging between 0.9 and 1.5. Following decalcification and staining of tissue sections, vesicular structures retain integrity by uptake of lead and uranium salts while collagen stains only poorly. Implications of these results are discussed with respect to the physicochemical and biological events of vertebrate calcification.

X-ray microanalysis of mineralized matrix vesicles of experimental saccular aneurysms

An energy dispersive X-ray microanalytical study was designed to examine the mineral deposits in matrix vesicles found in the walls of experimental aneurysms from two rabbits (103 and 1071 days postoperatively) and two sheep aneurysms (234 and 1202 days postoperatively). The freeze-substitution technique was adopted for use to retain inorganic ions in situ. Numerous, various sized extracellular electron-dense structures, believed to be matrix vesicles were observed. Size histograms for the mineralized vesicles showed that the proportion of smaller vesicles was higher in the older animals. A total of 370 vesicles were analyzed. Calcium and phosphorus with small amounts of magnesium were identified. No particular calcium phosphate mineral was dominant with the mean Ca/P molar ratio for all animals falling in the 1.1-1.2 range. Correlation coefficients for interrelationships between calcium, phosphorus, magnesium, and size were weak except for calcium vs phosphorus which was close to one, consistent with some type of calcium phosphate being the major constituent of the mineralized vesicles. Smaller electron-dense particles, probably mitochondrial granules were seen in some smooth muscle cells; a small number were analyzed and contained calcium and phosphorus (mean Ca/P molar ratio of 0.86) but no magnesium.

Demonstration of mitochondrial mineral deposits in osteoblasts after anhydrous fixation and processing

The fine structure of early developing bone was examined using a modification of a new non-aqueous processing method in which anhydrous glutaraldehyde dissolved in dimethylsulphoxide (GLUT-DMSO) is used as a fixative. Preliminary results show that the basic morphological features of the cellular and extracellular compartments of developing bone were preserved. The cytoplasm of osteoblasts revealed numerous well-preserved mitochondria and other membranous organelles. Inside the mitochondria there were large and conspicuous electron-opaque granules of mineral which were more prominent and numerous than in specimens prepared by conventional aqueous procedures. The collagenous matrix also revealed electron-opaque deposits of mineral. These results support the evidence for the existence of mitochondrial calcium phosphate in osteoblasts in the form of granules.

Cryoultramicrotomy as a preparative method for x-ray microanalysis in pathology

The role of ion shifts in cell injury has become one of the most intriguing fields of application of X-ray microanalysis in pathology. In principle, cryo(ultra)-microtomy is the best preparative method for X-ray microanalysis of diffusible substances. In this review, the following points are discussed: the choice of freezing method and coolant, the use of high molecular weight polymer cryoprotectants and their possible physiological effects the choice of the cryosectioning temperature, and techniques for handling and transfer of sections. Experiences with the sectioning of cryoprotected tissue are presented. Finally, other preparative techniques for microanalysis are compared to cryoultramicrotomy.

Levels of dinoflagellate chromosome-bound metals in conditions of low external ion availability: an x-ray microanalytical study

Cells of the dinoflagellate Glenodinium foliaceum were able to grow and divide in artificial (AE50) liquid culture medium diluted down to 10% of its normal concentration. X-ray microanalysis, with on-line computation of mass fractions, was used to determine the quantitative occurrence of bound (insoluble) elements in the chromosomes of cells grown in normal, 30 and 10% medium. In normal medium, chromosomes contained high levels of phosphorus (nucleic acid), sulphur (protein) and a variety of bound divalent metals, including Ca, Fe, Ni, Cu and Zn. With a decrease in the level of external ions (30 and 10% dilutions), the level of sulphur showed a significant decrease, but the mass fractions of insoluble phosphorus and total divalent metals did not fall. The presence of these metals in dinoflagellate chromatin does not, therefore, simply involve intracellular deposition in response to high external levels. The occurrence of divalent metals showed variation with medium concentration in terms of the proportions of different metals present, the nature of the metal--nucleoprotein associations, the metal concentrations per unit mass of chromatin and the number of metal atoms per 100 nucleotides. None of the above characteristics is therefore constant in an individual species.

Prospects of X-ray microanalysis in the study of pathophysiology of myocardial contraction

X-ray microanalysis was used to compare chemically untreated cryosections of quick-frozen myocardial tissue in "caffeine contracture" with cryosections of normal muscle. Our goal was to find out if it is possible by means of this method to detect changes in the calcium compartmentalization of the myocardial cell occurring by changes in its functional state. While it is possible to quantitate calcium in the cisternae of sarcoplasmic reticulum of the control muscle preparation, calcium could never be detected in these compartments of caffeine-contracted muscles. In active microsomal fraction of ventricular myocardium it is possible to quantitate calcium and also to distinguish two components on account of their different ability to accumulate this element. The calcium content is different in the two components of the fraction.