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Electromagnetic fields (EMF) might have various biological effects on the developing embryo. We studied the effects of pulsing electromagnetic fields (PEMF) on the in vitro development of preimplantation mouse embryos and of early somite rat embryos as well as on the in vivo development of rat embryos. We used PEMF at frequencies of 1, 20, 50, 70, and 100 Hz with a tension of 0.6 V/m. The embryos were exposed to PEMF throughout the experimental period. PEMF at frequencies of 20 and 50 Hz were embryotoxic, inhibiting over 50% of blastocysts from hatching and further development, all within 72 h of culture. PEMF at frequencies of 50 and 70 Hz induced 22% and 30% incidence of malformations in 10.5 day old rat embryos after 48 h in culture. The main malformations were absence of telencephalic, optic, and otic vesicles and of forelimb buds. In addition, retarded growth and development manifested by fewer somites, reduction in crown-rump length, and retarded closure of the neural tube were found in many embryos. No significant pathological changes were found by TEM in PEMF-exposed embryos. Disappearance of microvilli and collapse of apical parts of endodermal cells were observed by SEM in many yolk sacs of embryos exposed to 50 and 70 Hz PEMF. A slightly reduced litter average, a reduction or increase of weight, and a delay in eye opening was observed among offspring of pregnant rats exposed throughout pregnancy to PEMF at frequencies of 20, 50, and 100 Hz. No malformations were observed among these offspring. The mechanism of PEMF-induced embryotoxicity and teratogeneity is unknown, as is the mechanism of the "protective effects" of the mother on the rat embryos exposed to PEMF in vivo.
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PMID:Effects of pulsing electromagnetic fields on the prenatal and postnatal development in mice and rats: in vivo and in vitro studies. 221 43

The cytochemical localization of enzymatic activity by means of backscattered electron imaging (BEI) is reviewed and the application of BEI to changes in acid phosphatase and ATPase distribution during physiological (programmed) cell death in Heliothis midgut is explored. Programmed cell death entails the release of nascent free acid phosphatase as extracisternal hydrolase. This shift can readily be detected by means of the atomic number contrast imparted by BEI of the lead phosphatase reaction product, thus enabling the distribution of dying cells to be mapped. BEI is particularly useful in this context as it allows the examination of bulk specimens at low magnification. Death of cells is also accompanied by a collapse in ATPase activity which shows up as cytochemically negative areas in the X-ray microscope and by means of BEI. Acid phosphatase in normal cells is localized in the apical microvilli and lysosomes. Senescent or dying cells, however, clearly show a basally situated free hydrolase which migrates throughout the cell. Parallel TEM results confirm that this enzyme is ribosomal and extracisternal rather than lysosomal in origin. ATPase activity is largely limited to the apical microvilli, although there is some activity associated with the basal plasma membranes. The apical ATPase, however is partially resistant to ouabain. Young and mature cells are positive although in the latter case some microvilli may be lost as the cells acquire a negative cap or dome. Inhibition by bromotetramizole indicates that apical activity is not to any significant extent contributed to by alkaline phosphatase. Degenerate or dead cells are negative and can be seen as a mozaic of "black patches" among normal cells when imaged by means of BEI or X-ray microscopy.
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PMID:The use of backscattered electron imaging, X-ray microanalysis and X-ray microscopy in demonstrating physiological cell death. 297 76

During the late stages of cranial neurulation in mammalian embryos, the neural epithelium becomes concave. A thick subapical band of microfilament bundles, attached to junctions which are both vertical and horizontal in orientation, can be seen by TEM. Prior to this the neural epithelium is first biconvex and then V-shaped in transverse section, microfilament bundles are absent, and the subapical junctions are only vertical in orientation. In order to determine the role of microfilaments in cranial neurulation, rat embryos were exposed to cytochalasin D (0.15 micrograms ml-1) for 1 h at three stages of development: convex neural fold stage, early concave (prior to midline apposition at the forebrain/midbrain junction: 'preapposition') and later concave ('postapposition'). They were subsequently washed and cultured in addition-free medium for 5, 12, 24 or 36 h, then examined alive and by LM, TEM, or SEM. The degree of neural fold collapse varied with the stage of development: at the convex stage there was only slight opening out of the neural groove; early concave (preapposition) neural folds collapsed laterally to a horizontal position; later concave (postapposition) neural folds showed widening of the midbrain/hindbrain neuropore and slight neuroepithelial eversion at the anterior neuropore. Neural epithelium which had been concave prior to cytochalasin D treatment changed in structure so that the cells were broader and shorter; most of the subapical junctions were vertical in orientation, and microfilament bundles were represented either as a mass of amorphous material adjacent to the junctions, or as separated and broken filaments. Re-elevation of neural folds in 'recovery' cultures was accompanied by regeneration of apical microfilament bundles and horizontal junctions. Embryos which had been exposed to cytochalasin D at the convex or later concave stage of cranial neural fold development were able to complete cranial neural tube closure; none of the early-concave-stage embryos achieved apposition at the forebrain/midbrain junction, and all had major cranial neural tube defects. The results suggest that contraction of apical microfilament bundles plays an essential role in elevation of the neural folds and in the generation of concave curvature during the later stages of cranial neurulation. During the convex neural fold stage, microfilaments are important in maintaining neuroepithelial apposition in the neural groove, but are not crucial to maintenance of the convex shape. Successful formation and maintenance of the forebrain/midbrain apposition point at the appropriate time is considered to be essential for subsequent brain tube closure.
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PMID:The role of microfilaments in cranial neurulation in rat embryos: effects of short-term exposure to cytochalasin D. 407 37

The effect of the preparation steps of the TEM embedding procedure on the preservation of the Escherichia coli capsule was studied light microscopically. Electron microscopical micrographs did not distinctly reveal capsules whereas simultaneously performed India ink assays clearly revealed predominant capsules both on viable and on chemically fixed bacteria. It is clearly shown that dehydration does not cause extraction or collapse of capsular material to an extent that would explain the invisibility of the capsule on the electron microscopical level, as has hitherto been supposed.
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PMID:Fate of the Escherichia coli capsule during embedding procedures for electron microscopical studies. 616 40

Transplant quality human kidneys were sliced (approximately equal to 2 mm thick) and cortical regions further minced to approximately 1 mm3. These samples were treated successively with EDTA and detergents to solubilize cellular materials but leave the extracellular matrix (ECM), including basement membranes (BMs) intact. Resultant acellular cortices bear a remarkable resemblance to their in vivo counterparts. By light microscopy, patent, expanded tubular BM (TBM), peritubular capillary BM (PTCBM) and Bowman's capsule BM (BCBM) are surrounded by a swollen ECM which is occasionally fibrillar. Glomerular BM (GBM) lacks supporting interstitium but nevertheless remains convoluted and does not collapse. At the level of transmission electron microscopy, the diverse morphological characteristics of each BM type are evident. Random thickness measurements (lamina densa only) show that BCBMs are thickest (approximately equal to 2,400 nm) followed by TBMs (approximately equal to 750 nm), GBMs (approximately equal to 335 nm) and PTCBMs (approximately equal to 125 nm). Power transformations to normalize right-sided skew of thickness distribution curves reduce their arithmetic means 3-16%. SEM studies confirm LM and TEM observations that isolated GBMs maintain their free-standing spheroidal shapes and indicate that they may be intrinsically rigid. Moreover, their surface topographical details are preserved. We conclude that the acellular cortex offers a clarified view of renal interstitial morphology and demonstrates structural diversity among major renal BM types. Moreover, it provides a baseline of morphological information on which to assess pathological conditions of renal cortical extracellular matrix.
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PMID:Ultrastructure of isolated basement membranes in the acellular human renal cortex. 661 89

The degeneration of the capsule epithelium of cataractous lenses has been studied with LM, SEM en TEM with emphasis on TEM. The observed degeneration of the epithelial cells can be described as follows: The cell nucleus becomes picnotic and disintegrates as result of change of the chromatin. Degeneration of the cytoplasm starts with swelling of the mitochondria, coming into existence of filamentous networks and balloon-like bulges of the nucleus. Repelling of the cell nucleus due to a porosity of the plasma membrane. Collapse of the cell due to degeneration of the cell and loss of the cytoplasmic contents, leaving finally only a swollen framework of cell walls.
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PMID:Human capsule epithelial cell degeneration, A LM, SEM and TEM investigation. 818 28

The kinetics of refolding of TEM-1 beta-lactamase from solution in guanidine hydrochloride have been investigated on the manual and stopped-flow mixing time scales. The kinetics of change of far-UV circular dichroism and of intrinsic and ANS fluorescence have been compared with changes in the quenching of fluorescence by acrylamide as a probe of the accessibility of solvent to tryptophan. The binding of ANS points to hydrophobic collapse in the very early stages of folding which take place in the burst phase. This is accompanied by regain of 60-65% of native ellipticity, indicating formation of a significant proportion of secondary structure. Also in the burst phase, the tryptophan residues, which are largely exposed to solvent in the native protein, become less accessible to acrylamide, and the intrinsic fluorescence increases markedly. An early intermediate is thus formed in which tryptophan is more buried than in the native protein. Further intermediates are formed over the next 20 s. Quenching by acrylamide increases during this period, as the transient nonnative state is disrupted and the tryptophan residue(s) become(s) reexposed to solvent. The two slowest phases are determined by the isomerization of incorrect prolyl isomers, but double jump tryptophan fluorescence and acrylamide quenching experiments show little, if any, effect of proline isomerization on the earlier phases. Hydrophobic collapse thus occurs to a folding intermediate in which there is a nonnative element of structure which has to rearrange in the later steps of folding, resulting in a nonhierarchical folding pathway. The C-terminal W290 is suggested as being involved in the nonnative intermediate. beta-Lactamase provides further evidence for the occurrence of nonnative intermediates in protein folding.
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PMID:A collapsed intermediate with nonnative packing of hydrophobic residues in the folding of TEM-1 beta-lactamase. 948 21

This review traces some of the key features of the folding of beta-lactamases and their relevance to the way proteins fold in general. Studies on the enzymes have highlighted the nature and role of equilibrium and transient condensed states. The kinetics of folding are multiphasic, and when monitored by acrylamide quenching of the tryptophan fluorescence, an early phase provides evidence for the transient accumulation of a nonnative intermediate involving burial of tryptophan in a nonpolar environment. Intermediate phases can be understood in terms of progressive folding of different parts of the molecule. The later, slow phases are associated with proline isomerization in the TEM-1 enzyme and, in its P167T mutant form, with isomerization from trans to cis of the E166 T167 peptide bond. Coupled with kinetic and X-ray crystallographic studies of the beta-lactamase from Staphylococcus aureus and its D179Q mutant, it appears that the final stage of folding is that of collapse and packing of the omega-loop on to the main body of the protein.
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PMID:Beta-lactamases as models for protein-folding studies. 961 75

The respiratory system consists of morphologically and functionally distinct sub-divisions-the air-conditioning part and respiratory portion is were O2 and CO2 exchange actually occurs across the delicate, very thin walls of the pulmonary alveoli. The final bifurcation of bronchiole yields terminal bronchiole. The epithelium is gradually reduced from ciliated columnar in the larger bronchioles to ciliated or non-ciliated low cuboidal in the terminal segment. Here non-ciliated Clara cells are plentiful. Only under EM one can clearly identify the lining cells of the alveoli: type I are squamous pneumocytes, type II are large granular alveolar cells and macrophages (dust cells). The hallmarks of pneumocytes type II are the numerous osmiophilic, lamellated inclusion bodies. In TEM there is evidence connecting these bodies with the production of stabilizing surface active material, which prevents the collapse of the alveoli; colled surfactant, different from that of the Clara cells.
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PMID:[Histological structure of the distal segment of the respiratory tract]. 962 62

A prepration technique for nanometer particles, namely the replacing solvent drying technique, was developed. The main process of the technique including replacement of water in gel with special organic solvent and the removal of the solvent by distillation. No collapse of gel structure took place because of low interface tension between water and the solvent as well as low surface tension of the solvent. Where special apparatus and strictly limited preparation conditions were not necessary. The technique is noted for its low preparation cost and high universality. Titanium oxide and copper borate were prepared using the technique and were characterized using XRD, nitrogen physical adsorption, TEM, and small angle X-ray scattering. Results indicated that the titanium oxide and copper borate possessed particle sizes of 7-10 and 7-20 nm as well as a specific surface area of 235 m2/g and 360 m2/g, respectively. The specific surface area were even much higher than that of the samples prepared using supercritical drying technique. Copyright 1998 Academic Press.
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PMID:Replacing Solvent Drying Technique for Nanometer Particle Preparation. 984 79


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