Microincineration, electron microscopy, and electron diffraction of calcium phosphate-loaded mitochondria

Lithium isotopes differentially modify mitochondrial amorphous calcium phosphate cluster size distribution and calcium capacity

Lithium is commonly prescribed as a mood stabilizer in a variety of mental health conditions, yet its molecular mode of action is incompletely understood. Many cellular events associated with lithium appear tied to mitochondrial function. Further, recent evidence suggests that lithium bioactivities are isotope specific. Here we focus on lithium effects related to mitochondrial calcium handling. Lithium protected against calcium-induced permeability transition and decreased the calcium capacity of liver mitochondria at a clinically relevant concentration. In contrast, brain mitochondrial calcium capacity was increased by lithium. Surprisingly, 7Li acted more potently than 6Li on calcium capacity, yet 6Li was more effective at delaying permeability transition. The size distribution of amorphous calcium phosphate colloids formed in vitro was differentially affected by lithium isotopes, providing a mechanistic basis for the observed isotope specific effects on mitochondrial calcium handling. This work highlights a need to better understand how mitochondrial calcium stores are structurally regulated and provides key considerations for future formulations of lithium-based therapeutics.

Mitochondrial calcium at the synapse

Mitochondria are dynamic organelles, which serve various purposes, including but not limited to the production of ATP and various metabolites, buffering ions, acting as a signaling hub, etc. In recent years, mitochondria are being seen as the central regulators of cellular growth, development, and death. Since neurons are highly specialized cells with a heavy metabolic demand, it is not surprising that neurons are one of the most mitochondria-rich cells in an animal. At synapses, mitochondrial function and dynamics is tightly regulated by synaptic calcium. Calcium influx during synaptic activity causes increased mitochondrial calcium influx leading to an increased ATP production as well as buffering of synaptic calcium. While increased ATP production is required during synaptic transmission, calcium buffering by mitochondria is crucial to prevent faulty neurotransmission and excitotoxicity. Interestingly, mitochondrial calcium also regulates the mobility of mitochondria within synapses causing mitochondria to halt at the synapse during synaptic transmission. In this review, we summarize the various roles of mitochondrial calcium at the synapse.

Adenylate kinase derived ATP shapes respiration and calcium storage of isolated mitochondria

The ratio of ADP and ATP is a natural indicator of cellular bioenergetic state and thus a prominent analyte in metabolism research. Beyond adenylate interconversion via oxidative phosphorylation and ATPase activities, ADP and ATP act as steric regulators of enzymes, e.g. cytochrome C oxidase, and are major factors in mitochondrial calcium storage potential. Consideration of all routes of adenylate conversion is critical to successfully predict their abundance in an experimental system and to correctly interpret many aspects of mitochondrial function. We showcase here how adenylate kinases elicit considerable impact on the outcome of a variety of mitochondrial assays through their drastic manipulation of the adenylate profile. Parameters affected include cytochrome c oxidase activity, P/O ratio, and mitochondrial calcium dynamics. Study of the latter revealed that the presence of ATP is required for mitochondrial calcium to be shaped into a particularly dense form of mitochondrial amorphous calcium phosphate.

Mitochondrial Calcification

One of the most fascinating aspects of mitochondria is their remarkable ability to accumulate and store large amounts of calcium in the presence of phosphate leading to mitochondrial calcification. In this paper, we briefly address the mechanisms that regulate mitochondrial calcium homeostasis followed by the extensive review on the formation and characterization of intramitochondrial calcium phosphate granules leading to mitochondrial calcification and its relevance to physiological and pathological calcifications of body tissues.

Precipitation of Inorganic Salts in Mitochondrial Matrix

In the mitochondrial matrix, there are insoluble, osmotically inactive complexes that maintain a constant pH and calcium concentration. In the present paper, we examine the properties of insoluble calcium and magnesium salts, such as phosphates, carbonates and polyphosphates, which might play this role. We find that non-stoichiometric, magnesium-rich carbonated apatite, with very low crystallinity, precipitates in the matrix under physiological conditions. Precipitated salt acts as pH buffer, and, hence, can contribute in maintaining ATP production in ischemic conditions, which delays irreversible damage to heart and brain cells after stroke.

Mitochondrial Role in Cellular Mineralization

Light and electron microscopy followed by microincineration procedures on the cells of the growing deer antler tip showed a concentration gradient of granules as cell maturation proceeded from the primitive to the mature cell type. The distribution of the intramitochondrial granules in the various cell types suggested mitochondria in the initial phase of the mineralization process.

Role of inorganic polyphosphate in mammalian cells: from signal transduction and mitochondrial metabolism to cell death

Inorganic polyphosphate (polyP) is a polymer compromised of linearly arranged orthophosphate units that are linked through high-energy phosphoanhydride bonds. The chain length of this polymer varies from five to several thousand orthophosphates. PolyP is distributed in the most of the living organisms and plays multiple functions in mammalian cells, it is important for blood coagulation, cancer, calcium precipitation, immune response and many others. Essential role of polyP is shown for mitochondria, from implication into energy metabolism and mitochondrial calcium handling to activation of permeability transition pore (PTP) and cell death. PolyP is a gliotransmitter which transmits the signal in astrocytes via activation of P2Y1 receptors and stimulation of phospholipase C. PolyP-induced calcium signal in astrocytes can be stimulated by different lengths of this polymer but only long chain polyP induces mitochondrial depolarization by inhibition of respiration and opening of the PTP. It leads to induction of astrocytic cell death which can be prevented by inhibition of PTP with cyclosporine A. Thus, medium- and short-length polyP plays role in signal transduction and mitochondrial metabolism of astrocytes and long chain of this polymer can be toxic for the cells.

Mg(2+) differentially regulates two modes of mitochondrial Ca(2+) uptake in isolated cardiac mitochondria: implications for mitochondrial Ca(2+) sequestration

The manner in which mitochondria take up and store Ca(2+) remains highly debated. Recent experimental and computational evidence has suggested the presence of at least two modes of Ca(2+) uptake and a complex Ca(2+) sequestration mechanism in mitochondria. But how Mg(2+) regulates these different modes of Ca(2+) uptake as well as mitochondrial Ca(2+) sequestration is not known. In this study, we investigated two different ways by which mitochondria take up and sequester Ca(2+) by using two different protocols. Isolated guinea pig cardiac mitochondria were exposed to varying concentrations of CaCl2 in the presence or absence of MgCl2. In the first protocol, A, CaCl2 was added to the respiration buffer containing isolated mitochondria, whereas in the second protocol, B, mitochondria were added to the respiration buffer with CaCl2 already present. Protocol A resulted first in a fast transitory uptake followed by a slow gradual uptake. In contrast, protocol B only revealed a slow and gradual Ca(2+) uptake, which was approximately 40 % of the slow uptake rate observed in protocol A. These two types of Ca(2+) uptake modes were differentially modulated by extra-matrix Mg(2+). That is, Mg(2+) markedly inhibited the slow mode of Ca(2+) uptake in both protocols in a concentration-dependent manner, but not the fast mode of uptake exhibited in protocol A. Mg(2+) also inhibited Na(+)-dependent Ca(2+) extrusion. The general Ca(2+) binding properties of the mitochondrial Ca(2+) sequestration system were reaffirmed and shown to be independent of the mode of Ca(2+) uptake, i.e. through the fast or slow mode of uptake. In addition, extra-matrix Mg(2+) hindered Ca(2+) sequestration. Our results indicate that mitochondria exhibit different modes of Ca(2+) uptake depending on the nature of exposure to extra-matrix Ca(2+), which are differentially sensitive to Mg(2+). The implications of these findings in cardiomyocytes are discussed.

A review of phosphate mineral nucleation in biology and geobiology

Relationships between geological phosphorite deposition and biological apatite nucleation have often been overlooked. However, similarities in biological apatite and phosphorite mineralogy suggest that their chemical formation mechanisms may be similar. This review serves to draw parallels between two newly described phosphorite mineralization processes, and proposes a similar novel mechanism for biologically controlled apatite mineral nucleation. This mechanism integrates polyphosphate biochemistry with crystal nucleation theory. Recently, the roles of polyphosphates in the nucleation of marine phosphorites were discovered. Marine bacteria and diatoms have been shown to store and concentrate inorganic phosphate (Pi) as amorphous, polyphosphate granules. Subsequent release of these P reserves into the local marine environment as Pi results in biologically induced phosphorite nucleation. Pi storage and release through an intracellular polyphosphate intermediate may also occur in mineralizing oral bacteria. Polyphosphates may be associated with biologically controlled apatite nucleation within vertebrates and invertebrates. Historically, biological apatite nucleation has been attributed to either a biochemical increase in local Pi concentration or matrix-mediated apatite nucleation control. This review proposes a mechanism that integrates both theories. Intracellular and extracellular amorphous granules, rich in both calcium and phosphorus, have been observed in apatite-biomineralizing vertebrates, protists, and atremate brachiopods. These granules may represent stores of calcium-polyphosphate. Not unlike phosphorite nucleation by bacteria and diatoms, polyphosphate depolymerization to Pi would be controlled by phosphatase activity. Enzymatic polyphosphate depolymerization would increase apatite saturation to the level required for mineral nucleation, while matrix proteins would simultaneously control the progression of new biological apatite formation.

Mitochondrial Ca2+ sequestration and precipitation revisited

The ability of mitochondria to sequester and retain divalent cations in the form of precipitates consisting of organic and inorganic moieties has been known for decades. Of these cations, Ca(2+) has emerged as a major player in both signal transduction and cell death mechanisms, and, as a consequence, the importance of mitochondria in these processes was soon recognized. Early studies showed considerable effort in identifying the mechanisms of Ca(2+) sequestration, precipitation and release by uncouplers of oxidative phosphorylation; however, relatively little information was obtained, and these processes were eventually taken for granted. Here, we re-examine: (a) the thermodynamic aspects of mitochondrial Ca(2+) uptake and release, (b) the insufficiently explained effect of uncouplers in inducing mitochondrial Ca(2+) release, (c) the thermodynamic effects of exogenously added adenine nucleotides on mitochondrial Ca(2+) uptake capacity and precipitate formation, and (d) the elusive nature of the Ca(2+) -phosphate precipitates formed in the mitochondrial matrix.

The relationship between calcium accumulation in osteoclast mitochondrial granules and bone resorption

In the process of bone resorption, calcium is considered to be transported within vesicles in osteoclasts and eventually released. We studied the ultramicromorphology of calcium (Ca) transport in osteoclasts by preparing samples of osteoclasts collected from rat femurs in which calcium was maximally preserved and subjected them to high-pressure quick-freezing and freeze-substitution. We then examined the localization of calcium by Electron Energy Loss Spectroscopy (EELS). The structures of cell membranes were preserved, suggesting the suitability of this high-pressure quick-freezing and freeze-substitution technique. Osteoclast mitochondria adjacent to the ruffled border were rich in mitochondrial granules and contained a large amount of Ca. In contrast, mitochondria in the basolateral region contained few granules. Moreover, by an osteoclast-culturing experiment, differences in the morphology of mitochondrial granules were noted between culturing on a dentin slice and that on a gold plate, i.e., few mitochondrial granules were noted in osteoclasts cultured on a non-dentin plate. These findings suggest an association between the morphology of mitochondrial granules in osteoclasts and bone resorption as well as a new transport route for Ca resorbed by osteoclasts. We propose that Ca accumulates in mitochondria granules to prevent increased Ca concentration in cytoplasm of osteoclasts during bone resorption.

Amorphous calcium phosphate in casein micelles of bovine milk

The calcium phosphate remaining after hydrazine deproteination of casein micelles isolated from bulk skim milk exhibits under the electron microscope a very fine and uniform granularity being formed by small subunits with a true diameter of approximately 2.5 nm. This material, which is about 10 percent by weight citrate, termed calcium phosphate citrate (CPC) complex, also contains Mg and Zn at molar ratios of 0.03 and 0.003 respectively. Radial distribution function (RDF) and infrared analyses show that CPC is a Mg-containing amorphous calcium phosphate (ACP) similar to synthetic and cytoplasmic ACP. presence of CPC in casein micelles as an amorphous colloid bonded with phosphoproteins provides the means for storing in milk large amounts of Ca (16 mM) and Pi (10 mM) in a readily utilizable form but at a higher ion concentration than found in biological solutions.

Calcium-containing lysosomes in the outer mantle epithelial cells of Amblema, a fresh-water mollusc

The cells of the outer mantle epithelium contain numerous large pleomorphic electron dense bodies. In their fine structure they resemble lysosomes. Positive acid phosphatase histochemistry confirms that these supranuclear and subnuclear structures are lysosomes. A major portion of the intralysosomal material is resistant to high-temperature microincineration, indicative of an inorganic component. Subsequent microprobe analyses identified considerable calcium within these organelles. Such entities are similar in structure and ionic content to the lysosomes of avian intestinal absorbing cells, another calcium-transporting epithelium. These mantle lysosomes may function in transcellular calcium transport during shell formation, growth, and repair, especially since the mantle is the shell-forming organ in molluscs.

An electron microscopic histochemical and X-ray microprobe study of spherites in a mussel

Transmission electron microscopic, histochemical and X-ray analytical microprobe techniques were used to study the inorganic-organic relationship in the spherites (calcospherules) from the mantle, i.e. subadjacent to the outer mantle epithelium, of the fresh-water mussel Amblema. These structures were shown to contain calcium which could be chelated by the flotation of sections on solutions of either formic acid or ethylene glycol bis-(beta-amino ethyl ether)-N, N1-tetra-acetic acid (EGTA), Analysis of both non-chelated and sections revealed a significant sulfur peak. Chelated spherites were also intensely stained with acid phosphotungstic acid (PTA), Such data is indicative of the presence of an organic glycoprotein (proteoglycan) matrix which could serve to bind mineral ions, thus forming organic-inorganic aggregates for calcium transport and homeostasis. In this regard, the spherites are analogous to both calcium phosphate containing mitochondrial granules and the initial calcification sites in vertebrate mineralizing tissues.

The correlation between bismuth and uranyl staining and phosphorus content of intracellular structures as determined by electron spectroscopic imaging

Four groups of intracellular structures can be recognized according to bismuth and uranyl staining and phosphorus content. (1) Those which contain phosphorus and stain strongly with uranyl acetate but not with bismuth (ribosomes, heterochromatin and mature ribosomal precursor granules), presumably because of their nucleic acid content. (2) Those which contain phosphorus and stain with uranyl acetate and bismuth (interchromatin granules, immature ribosomal precursor granules and mitochondrial granules), presumably because at least some of their phosphate is available to react with bismuth. (3) Those which contain little phosphorus but which stain strongly with bismuth and weakly with uranyl acetate (Golgi complex beads), perhaps because some ligand in addition to phosphate reacts with bismuth, and (4) those which do not contain phosphorus and stain with neither uranyl acetate nor bismuth (portasomes). Uranyl staining correlates strongly with the phosphorus content of nucleic acids, proteins and inorganic deposits. Bismuth will stain some phosphorylated molecules but not all. Thus only some phosphates stain with bismuth.

Phosphocitrate inhibits mitochondrial and cytosolic accumulation of calcium in kidney cells in vivo

Synthetic 3-phosphocitrate, an extremely potent inhibitor of calcium phosphate crystallization as determined in a nonbiological physical-chemical assay, has many similarities to a mitochondrial factor that inhibits crystallization of nondiffracting amorphous calcium phosphate. In order to determine whether phosphocitrate can prevent uptake and crystallization of calcium phosphate in mitochondria in vivo, it was administered intraperitoneally to animals given large daily doses of calcium gluconate or parathyroid hormone, a regimen that causes massive accumulation and crystallization of calcium phosphate in the mitochondria and cytosol of renal tubule cells in vivo. Administration of phosphocitrate greatly reduced the net uptake of Ca2+ by the kidneys and prevented the appearance of apatite-like crystalline structures within the mitochondrial matrix and cytosol of renal tubule cells. Phosphocitrate, which is a poor chelator of Ca2+, did not reduce the hypercalcemia induced by either agent. These in vivo observations therefore indicate that phosphocitrate acts primarily at the cellular level to prevent the extensive accumulation of calcium phosphate in kidney cells by inhibiting the mitochondrial accumulation or crystallization of calcium phosphate.

Electron probe analysis of cultured vascular smooth muscle

Mitochondrial and cytoplasmic composition were determined with electron probe analysis in freeze-dried guinea pig aortic smooth muscle cells cultured on stainless steel grids. The mitochondrial calcium content in normal cells was low: not significantly different from that detected in the cytoplasm. Mitochondrial calcium granules were found in less than 3% of the cells, and in these the cytoplasmic K/Na ratio was reduced, indicating that they were damaged. There were no major differences between the cytoplasmic concentrations of K, Cl, Ca, Mg, and S of cultured cells and those previously found in adult vascular smooth muscle (Somlyo et al '79). There was no evidence of nuclear Na or Ca sequestration in cultured cells, and the transmitochondrial Na, Cl, and K gradients were small. Attempts to selectively remove adhering, extracellular ions with a 2-second wash with isotonic ammonium acetate were unsuccessful because they were accompanied by loss of cell K.

Calcium deposition in human pituitary adenomas studied by histology, electron microscopy, electron diffraction and X-ray spectrometry

The incidence and morphogenesis of calcification were investigated by histology, electron microscopy, electron diffraction and X-ray spectrometry in 312 surgically removed human pituitary adenomas. By light microscopy the incidence of calcification was 9%. The calcium deposits were evident in several adenoma types, but were most frequent and extensive in prolactin-producing adenomas. Histologically calcium deposits represented amorphous precipitates and psammoma bodies staining with hematoxylin, the von Kossa technique and alizarin red. By electron microscopy, calcified deposits were noted in the cytoplasm of adenoma cells and extracellular space. Electron diffraction and X-ray spectrometry of intracellular precipitates as well as psammoma bodies showed the presence of phosphate, calcium and organically bound sulphur with a ratio of 3.5:5:2, indicating that they contained calcium hydroxyapatite. Present findings provide evidence that mitochondria with microcrystal deposition of calcium represent the primary sites of calcification.

Selective mitochondrial degeneration in renal tubules following hyperbaric oxygen exposure

To study the ultrastructural effects of hyperoxia on the kidney, young adult Sprague Dawley rats were exposed to 3 atmospheres absolute (ATAs) of pure oxygen for 5 hours and were killed in a time sequence varying from immediately to 30 days after exposure. Their renal cortices were processed for electron microscopy. Selective mitochondrial changes were observed within sublethally and transiently altered proximal tubular epithelial cells. The most consistent finding was the accumulation of 0.08 mu to 0.5 mu round to ovoid homogeneous matrical inclusions which frequently formed larger confluent amorphous masses. The inclusions stained intensely with lead and uranium but appeared homogeneously electron-lucent in unstained sections. Energy-dispersive x-ray analysis revealed that they did not contain calcium or phosphorus. The inclusions were different from the innately electron-opaque flocculent densities commonly found in pathologically altered mitochondria. Since the mitochondria containing them were removed by autophagocytosis, it is suggested that the inclusions were associated with selective mitochondrial degeneration induced by hyperoxia. No glomerular lesions were found.

Ultrastructure of cel organelles by scanning electron microscopy of thick sections surface-etched by an oxygen plasma

Kidney tissue double fixed in glutaraldehyde and osmium tetroxide and embedded in epoxy resin by standard techniques used for transmission electron microscopy was cut into section 1 micron or more thick and surface-etched by an oxygen plasma. Etching caused ash residues (possibly composed partly or organo-metallic complexes) of membranes and other etch resistant cell components to emerge as recognizable structures projecting upward from the surrounding embedment which was combusted and removed as volatile products. using the secondary electron mode for image formation, structural features of cells which could be imaged with clarity with the scanning electron microscopy included: profiles of peripheral and in-folded plasma membranes, the nuclear envelope and profiles of cut mitochondrial matrix granules, cristae and the outer limiting membranes. Resolution was better than that obtainable from most other methods of specimen preparation currently being used in scanning electron microscopy for viewing the internal structures of cells or organelles in bulk samples of tissue.

Calcium containing lysosomes in the normal chick duodenum: a histochemical and analytical electron microscopic study

Absorptive cells of the normal chick duodenum contain numerous supranuclear vesicular/vacuolar structures. By routine transmission electron microscopy, such structures are membrane bound and demonstrate a granular content. These vesicles appear to move laterally and eventually coalesce with the lateral plasma membrane (exocytosis). The granular contents are resistant to high temperature microincineration, thus revealing their mineral-containing nature. The granular vesicular matrix also stains intensely with osmium pyroantimonate EGTA chelation of pyroantimonate-stained vesicles selectively extracts the granules indicating a high concentration of calcium. X-ray microanalysis also demonstrates a significant intravesicular calcium localization. When tissues were incubated for the presence of acid phosphatase, the supranuclear vesicles were markedly positive for this lysosomal enzyme. A possible role for these calcium-containing lysosomes in the transcellular flux of calcium ions across the intestinal absorptive cell is discussed.

Intracellular and intramitochondrial binding of lanthanum in dark degenerating midgut cells of a collembolan (insect)

Lanthanum is known to be a marker of extracellular spaces. Intracellular organelles are always devoid of stain. But dark and damaged cells may be entered by the marker, as studied at the cellular level, using the electron probe X-ray microanalyser. The technique may be used to detect increased permeability at a stage when no fine structural abnormality is discernible.

A proposed cellular mechanism for calcium transport in the intestinal epithelial cell

Intracellular transport of calcium from the apical to the basal-lateral region of the intestinal epithelial cell was investigated in duodenum from normal fed, fasted, and calcium-loaded rats. The process was followed with time using electron microscopy with potassium pyroantimonate to precipitate calcium. The observations made were subjected to morphometric analysis. The specificity of the method was demonstrated in the villus cell by resistance to microincineration and by absence of deposits following exposure to EGTA. Using this method calcium was seen in cells from calcium-fed rats at the microvillus border, in the Golgi zone, and within the internal compartments of the mitochondria. In cells from fasted rats calcium was not seen. Mitochondria were found largely at the apex of the cell and were free of detectable calcium. By 5 min, in the cells of fasted rats given a calcium load, the calcium had reached the Golgi apparatus and the inner mitochondrial compartment. After 15 min mitochondria were heavily loaded with calcium and had moved to the basal region of the cell. These observations suggest that mitochondria play an important role in absorption of calcium and appear to transport this ion from the apex to the basal region of the cell where entry into the capillaries takes place.

X-ray microanalysis of epon sections after oxygen plasma microincineration

Dark-gold sections of osmium tetroxide-fixed, Epon-embedded brown adipose tissue before and after low-temperature oxygen plasma microincineration were examined using a high-resolution scanning transmission electron microscope and an energy-dispersive X-ray spectrometer. Microincineration produced ash patterns which were free of organic matrix, chlorine (from the Epon) and probably osmium (from the fixative). X-ray sensitivity was improved by a factor of 2-4 owing to decreased background, and sulphur, calcium and probably phosphorus were detected in the ash. Fidelity of the ash patterns permitted microanalytical spatial resolution of 0.1 micrometer or better. Oxygen plasma microincineration is thus shown to offer advantages for high resolution X-ray microanalysis of conventionally sectioned biological material. Its future application to shock-frozen, frozen-dried, unstained sections is indicated.

Fluoride-induced mineralization within vacuoles in maturative ameloblasts of the rat

Dense crystalline deposits appeared within vacuoles in rat maturative ameloblasts as a result of repeated injections of sodium fluoride. The crystals assumed varied arrangements but were always observed within intracellular vacuoles. The crystals resemble those of normal enamel and resist microincineration. They are readily dissolved by decalcification and leave behind an organic framework which matches the outline of the crystals. An experimental model is presented which may be useful in further studies of calcium transport, enamel matrix absorption or digestion of cellular debris.

Paramagnetic and crystallographic effects of low temperature ashing on human bone and tooth enamel

Low temperature ashing by excited gas (LTA) causes crystallographic and paramagnetic alterations of the human bone and tooth enamel mineral. On the one hand, LTA induces variations of the alpha lattice parameter. These variations depend upon the nature of the gas used, but are little affected by its degree of excitation. Trapping of gas molecules in the crystal structure is demonstrated. On the other hand, LTA produces two preponderant paramagnetic centers in bone and enamel samples at 20 degrees C. Their inorganic origin clearly indicated. One of the two radicals has been identified as O3- (g1 = 2.002, g2 = 2.010, g3 = 2.016) and the other as (CO3-3 (parallel = 1.996, g = perpendicular 2.003). Variations of the alpha lattice parameter and trapping of paramagnetic gas species do not seem to be directly related.

Scanning electron microscopical study on the fluorosis of enamel in rats

Sixteen 28-day-old male rats of Wistar strain, with a mean body weight of 179 g, were divided into two equal groups. Each group of eight animals was maintained for 70 days on drinking water, ad lib., containing no fluorine (control group) and 100 ppm of fluorine (experimental group). All specimens examined were obtained from the incisal portions of the incisors. The following types of enamel specimens were prepared for scanning electron microscopy: (1) acid-etched specimens; (2) acid-etched specimens followed by low temperature microincineration; and (3) fractured specimens. The enamel formed during high fluoride exposure showed marked hypocalcification, that is, the crystallite density in the prism core and interprismatic region was lower than that of control animals. The organic substances appeared to increase in these regions. The changes were prominent in the outer and middle enamel layers. Such changes following fluoride administration appear to indicate an inhibition of enamel maturation, that is, an inhibition of the mineral deposition and/or an inhibition of organic matrix withdrawal.

Mitochondrial granule distribution in tooth germ cells

Incisor and molar tooth germs of albino rats sacrificed at the eighteenth and twentieth days in utero and one to seven days after birth were studied with light and electron microscopy. Observations of the various stages of tooth development in molars established that intramitochondrial granules in odontoblasts were comparable to the intramitochondrial granules of other hard tissue cells. These electron-dense deposits appeared in mitochondria in an appreciable number only when odontoblasts become engaged in dentin mineralization. When dentin mineralization was advanced the odontoblast mitochondria appeared devoid of these deposits. Mesenchymal cells and preodontoblasts of the pulp were not involved in this activity.

The fine structure of the interrenal cells of the duck (Anas platyrhynchos) with evidence for possible exocytotic release of steroids

The duck interrenal cell possesses ultrastructural characteristics common to other steroid-secreting cells. Lipid droplets and mitochondria are abundant and lie principally at the apical end of the cell. Lipid droplets are not membrane-limited. Cisternae of smooth endoplasmic reticulum that are occasionally continuous with the less abundant rough endoplasmic reticulum are a prominent feature of the interrenal cell. Tubular profiles of rough endoplasmic reticulum often lie tangentially to mitochondria and ribosomes are either free, grouped in polyribosomal clusters, or bound to the endoplasmic reticulum. Mitochondria possess tubular cristae in the inner regions of the gland and frequently contain a paracrystalline array of small 10nm (o.d.) tubules and less frequently a hexagonal array of 40 nm trilaminar rings. Other cytoplasmic components include dense bodies, residual bodies, microtubules, microfilaments and specialized single membrane-bound vesicles. Gap junctions, intermediate junctions and interdigitating processes constitute the main intercellular associations. No tight junctions were identified. The single membrane-bound vesicles which are occasionally filled with a low electron-dense, lipid-like material form septate-like "junctions" with the plasma membrane. The septa bridge an intracellular gap of 15-17 nm. The vesicles are usually located near the subendothelial space at the basal and basilateral regions of the cell. Occasionally, vesicles fuse with the plasma membrane. It is suggested that these vesicles represent morphological evidence for the exocytotic release of steroid hormones.

Secretory hyperactivity and mitochondrial changes in neurosecretory cells of an insect. Cellular effects of the insecticide lindane

The neurosecretory cells of the corpus cardiacum of the desert locust Schistocerca gregaria secret their hormonal products by exocytosis. The insecticide lindane is known to cause release of hyperglycaemic but adipokinetic neurohormones. Electron microscopy of lindane-poisoned corpora cardiaca reveals many exocytotic omega figures. Mitochondria are affected either directly by the poison or by the consequences of secretory hyperactivity. They occur in increased number, divide, acquire dense mitochondrial granules larger than in the controls, and sometimes line up along plasma membranes, mitochondria in two neighbouring cells forming pairs in juxtaposition. Between two such mitochondria the plasma membranes form a junction-like structure. It is suggested that these effects reflect an excessive calcium entry caused by lindane.

X-ray microanalysis of mitochondrial deposits in ischemic myocardium

The x-ray microanalysis technique was used to determine the chemical composition of intramitochondrial electron-dense deposits in ischemic myocardial cells. Semi-thin sections were cut from Araldite-embedded tissue and analyzed in a scanning electron microscope equipped with energy- and wavelength-dispersive spectrometers. The energy dispersive spectrum revealed calcium and phosphorus peaks over many mitochondrial deposits. Peak to background ratios of calcium, phosphorus and magnesium obtained with the wavelength dispersive spectrometer were 1.7, 8.8 and 1.2, respectively. There was no consistent relationship in the characteristic peaks of calcium and phosphorus in a given mitochondrial granule. Magnesium appears to be negligible, except in some mitochondrial deposits which lacked calcium, where it was present with a peak to background ratio of two. These results suggest formation of calcium or magnesium phosphate in the mitochondria during ischemia. X-ray microanalysis can provide detailed information on subcellular electrolyte distribution in normal and ischemic myocardial cells and should be attempted with improved methods of tissue preparation.

Cations in the rat pars distalis ultrastructural localization

Pituitary glands of female Sprague Dawley rats were fixed using the potassium pyroantimonate-osmium tetroxide technique by immersion or vascular perfusion. Both fixation procedures resulted in similar patterns of cation localization visualized as electron-dense precipitate within cells of the pars distalis. Nuclei were prominent sites of localization. Cytoplasmic precipitate occurred in association with the endoplasmic reticulum, typically within the cisternal spaces, and also was localized within the mitochondrial matrix and cristae, as well as Golgi membranes, small Golgi-associated vesicles, and multivesicular bodies. Immature secretory granules often contained precipitate between the core material of the granule and the enclosing smooth membrane. Frequently small antimonate-containing vesicles bordered the immature secretory granules. Precipitate was variable in secretory granules of more mature appearance although precipitate was apparent occasionally just within a granule's enclosing membrane. Granules closest to the plasma membrane often contained increased amounts of precipitate and small vesicles containing precipitate were observed fusing with them. Instances of granule release by emiocytosis often revealed a clustering of precipitate behind the core material away from the emiocytotic stoma, as well as at the stoma, and frequently an increased electron density of filamentous material radiating from the granules' enclosing membranes or from the adjacent plasma membrane. Exposure of section material to the chelating agents EGTA and EDTA indicate that calcium is the primary cation localized within the cytoplasm of these secretory cells. These findings are consistent with a role for calcium as a facilitator in the processes of transport and release of secretory granules.

Ultrastructural alterations in skeletal muscle fibers of streptozotocin-diabetic rats

The ultrastructure of fast-twitch-oxidative-glycolytic (FOG), fast-twitch-glycolytic (FG) and slow-twitch-oxidative (SO) fibers in plantaris and soleus muscles of normal and streptozotocin-diabetic rats was studied. In the diabetic animals, the mitochondria of FOG and SO fibers showed a loss of cristae and an increase in electron-dense granules. There was also an increased number of lipid droplets in close proximity to the mitochondria and the nuclei, and a separation of individual muscle nuclei to form satellite cells. Higher incidences of surface projections and sarcoplasmic splittings at the nuclear region were noticed in SO fibers. The FG fibers showed some disorientation of the T-tubular system. It is concluded that streptozotocin-diabetes has differential effects on the fine structure of the three fiber types of rat skeletal muscle.

Low-temperature ashing of bovine dentine

The present studies were performed to obtain data on the low-temperature ashing (lta of dentine. Observations of colour and acid solubility, measurement of weight loss, and chemical analyses of carbon, hydrogen, and nitrogen assessed the ashing efficiency. The LTA method was sufficient to deproteinize dentine powder below 300 mesh. The determinations of calcium, magnesium, and phosphorus in dentine showed no significant differences between LTA, muffle furnace ashing (MFA), and wet ashing. The carbonate content was not significantly different after drying and LTA, but apporximately 48% carbonate was lost using MFA. X-ray diffraction patterns of dentine powder showed no detectable changes before and after LTA treatment compared to the patterns after treatment by MFA and/or ethylenediamine extraction.

Biochemical and ultrastructural aspects of Ca2+ transport by mitochondria of the hepatopancreas of the blue crab Callinectes sapidus

Mitochondria isolated from the hepatopancreas of the blue crab Callinectes sapidus show up to 12-fold stimulation of respiration on addition of Ca(2+), which is accompanied by Ca(2+) accumulation (Ca(2+):site = 1.9) and H(+) ejection (H(+):Ca(2+) = 0.85). Sr(2+) and Mn(2+) are also accumulated; Mg(2+) is not. A strongly hypertonic medium (383 mosM), Mg(2+), and phosphate are required for maximal Ca(2+) uptake. Ca(2+) uptake takes precedence over oxidative phosphorylation of ADP for respiratory energy. Once Ca(2+) is accumulated by the crab mitochondria, it is stable and only very slowly released, even by uncoupling agents. ATP hydrolysis also supports Ca(2+) uptake. Respiration-inhibited crab hepatopancreas mitochondria show both high-affinity and low-affinity Ca(2+)-binding sites, which are inactive in the presence of uncoupling agents. Crab hepatopancreas mitochondria have an enormous capacity for accumulation of Ca(2+), up to 5,500 ng-atoms Ca(2+) per mg protein, with an equivalent amount of phosphate. Freshly isolated mitochondria contain very large amounts of Ca(2+), Mg(2+), phosphate, K(+), and Na(+); their high Ca(2+) content is a reflection of the vary large amount of extra-mitochondrial Ca(2+) in the whole tissue. Electron microscopy of crab mitochondria loaded with Ca(2+) and phosphate showed large electron-dense deposits, presumably of precipitated calcium phosphate. They consisted of bundles of needle-like crystals, whereas Ca(2+)-loaded rat liver mitochondria show only amorphous deposits of calcium phosphate under similar conditions. The very pronounced capacity of crab hepatopancreas mitochondria for transport of Ca(2+) appears to be adapted to a role in the storage and release of Ca(2+) during the molting cycle of this crustacean.