Phialophora repens, an emerging agent of subcutaneous phaeohyphomycosis in humans

A 63-year-old Japanese man had phaeohyphomycosis that occurred as a solitary subcutaneous nodule on the dorsal aspect of his left hand. In the nodule there were foci of mixed granulomatous and suppurative infiltrations circumscribed by thick fibrous tissue reaction. The foci contained short septate hyphae and occasionally small rounded aggregates of irregularly branched septate hyphae, both of which were nonpigmented or rarely weakly pale brown. Fungal culture from the nodule was positive for a dematiaceous mold. The mycologic features of the mold were typical of Phialophora repens. The infection was successfully treated by excision of the nodule. This is the second reported case of infection due to P. repens.

Microinterferometry of the movement of dry matter in fibroblasts

We describe the use of interferometric microscopy coupled with a novel application of Senarmont compensation for detecting and quantifying the distribution of dry matter in cultured cells. In conjunction with video techniques and digital image processing, a two-dimensional, calibrated map of the dry mass distribution in an isolated cell can be obtained and digitally recorded. We have called the technique Digitally Recorded Interferometric Microscopy with Analyser Shift (DRIMAS). The method greatly facilitates the automatic recognition of cells by computer. Recorded time-lapse sequences can be used to establish a database of the growth and motility of specific cells in given experimental conditions. Databases of this type can be analysed to reveal the patterns of growth and locomotory behaviour of individual cells. We describe a systematic method of obtaining parameters of cell size, shape, spreading, intracellular motility and translocation. Auto-correlations and cross-correlations between these parameters can be detected and quantified using time series analysis, revealing potential cause/effect relationships in the mechanisms of growth and motility. Besides characterizing the overall pattern of cell behaviour, these data can also yield information about the instantaneous pattern of intracellular motility. We describe the use of finite element analysis to reveal the dynamics of the intracellular transport of dry matter. This yields the pattern of the minimum flow of dry matter required to account for the changes in its distribution. Most of this flux is not associated with the movement of visible structures and possibly represents the transport of dissociated components of the cytoskeleton. In chick heart fibroblasts, surprisingly high velocities of nearly 2.0 microns s-1 were detected during the period of increased motility following tail detachment. The total kinetic energy associated with the dry mass flux is a single parameter, which characterizes the instantaneous motility of the cell. We found that the kinetic energy of intracellular motility can be several hundred times greater than the kinetic energy of translocation. Kinetic energy may prove to be a very informative single measure of intracellular motility for assessing the effects of malignant transformation, genetic manipulations, and other experimental treatments on the locomotory machinery of the cell.

Asymmetric behavior of severed microtubule ends after ultraviolet-microbeam irradiation of individual microtubules in vitro

The molecular basis of microtubule dynamic instability is controversial, but is thought to be related to a "GTP cap." A key prediction of the GTP cap model is that the proposed labile GDP-tubulin core will rapidly dissociate if the GTP-tubulin cap is lost. We have tested this prediction by using a UV microbeam to cut the ends from elongating microtubules. Phosphocellulose-purified tubulin was assembled onto the plus and minus ends of sea urchin flagellar axoneme fragments at 21-22 degrees C. The assembly dynamics of individual microtubules were recorded in real time using video microscopy. When the tip of an elongating plus end microtubule was cut off, the severed plus end microtubule always rapidly shortened back to the axoneme at the normal plus end rate. However, when the distal tip of an elongating minus end microtubule was cut off, no rapid shortening occurred. Instead, the severed minus end resumed elongation at the normal minus end rate. Our results show that some form of "stabilizing cap," possibly a GTP cap, governs the transition (catastrophe) from elongation to rapid shortening at the plus end. At the minus end, a simple GTP cap is not sufficient to explain the observed behavior unless UV induces immediate recapping of minus, but not plus, ends. Another possibility is that a second step, perhaps a structural transformation, is required in addition to GTP cap loss for rapid shortening to occur. This transformation would be favored at plus, but not minus ends, to account for the asymmetric behavior of the ends.

In vitro studies of the thyroglobulin degradation pathway: endocytosis and delivery of thyroglobulin to lysosomes, release of thyroglobulin cleavage products--iodotyrosines and iodothyronines

Iodinated thyroglobulin stored in the thyroid follicular lumen is subjected to an internalization process and thought to be transferred into the lysosomal compartment for proteolytic cleavage and thyroid hormone release. In the present study, we have designed in vitro models to study: 1) the transfer of endocytosed thyroglobulin into lysosomes, and 2) the intracellular fate of free thyroid hormones and iodinated precursors generated by intralysosomal proteolysis of thyroglobulin. Open follicles prepared from pig thyroid tissue by collagenase treatment were used to probe the delivery of exogenous thyroglobulin to lysosomes via the differentiated apical cell membrane. Open follicles were incubated with pure [125I]thyroglobulin with or without unlabeled thyroglobulin in the presence or in the absence of chloroquine. Subcellular fractionation on a Percoll gradient showed that [125I]thyroglobulin was internalized and present in low (for the major part) and high density thyroid vesicles. In chloroquine-treated open follicles, we observed the appearance of a definite fraction of [125I]thyroglobulin in a lysosome subpopulation having the expected properties of phagolysosomes or secondary lysosomes. In contrast, in control open follicles, the amount of [125I]thyroglobulin or degradation products found in high density vesicles was lower and associated with the bulk of lysosomes, i.e., primary lysosomes. The content in thyroglobulin and degradation products of lysosomes at steady-state was analyzed by Western blot using polyclonal anti-pig thyroglobulin antibodies. Under reducing conditions, immunoreactive thyroglobulin species correspond to polypeptides with molecular weights ranging from 130,000 to less than 20,000. The presence of free thyroid hormones and iodotyrosines inside lysosomes and their intracellular fate was studied in dispersed thyroid cells labeled with [125I]iodide. Neo-iodinated [125I]thyroglobulin gave rise to free [125I]T4 which was secreted into the medium. In addition to released [125I]T4, a fraction of free [125I]T4 was identified inside the cells. Lysosomes isolated from dispersed thyroid cells did not contain significant amounts of free [125I]T4. The free intracellular [125I]T4 fraction seems to represent an intermediate 'hormonal pool' between thyroglobulin-bound T4 and secreted T4. Evidence for such a precursor-product relationship was obtained from pulse-chase experiments.

IN CONCLUSION

1) open thyroid follicles have the ability to internalize thyroglobulin by a mechanism of limited capacity and to address the endocytosed ligand to lysosomes.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure of the so-called 'prismless' enamel in human deciduous teeth

The surface enamel of human deciduous teeth showing a more negative birefringence by polarized light was investigated by differential interference contrast microscopy and by scanning electron microscopy (SEM) following EDTA etching. Though this surface enamel has been generally called the 'prismless' enamel, in this study, the so-called 'prismless' enamel was categorized into 'false', 'moderate', 'essential' and 'complex' types according to whether they took the form of distinct prisms which bended at the subsurface, indistinct circularly based prisms or not. Based on the SEM observations some types of the 'prismless' enamel showed parallel crystallites and no prism boundaries. However, if indistinct prisms showing centripetal crystallites within the circular boundaries are admitted into the prismless enamel, other types except the 'false' one will generally belong to it.

Mechanical and morphological effects of strain rate on fatigue of compact bone

Compact bone specimens were cyclically loaded in uniaxial tension for one million cycles; loading was performed at either of two physiological strain rates (0.01 s-1 or 0.03 s-1) and a physiological strain range (0-1200 microstrain). Microdamage in loaded and nonloaded control specimens was then assessed histomorphometrically. Fatigue, evidence by stiffness loss, was observed at both strain rates and was significantly greater in specimens loaded at the high experimental strain rate than in specimens loaded at the low strain rate. Morphologically, this fatigue corresponded to increased numbers of microcracks in the bone. These data show that fatigue and resultant microdamage are realistic expectations of cyclic loading within the physiological strain range. The rate at which strains are developed influences the fatigue behavior of compact bone, suggesting that cyclic loading at high physiological strain rates, characteristic of vigorous activities, is more damaging to compact bone than loading at lower physiological strain rates.

Myofibril assembly is linked with vinculin, alpha-actinin, and cell-substrate contacts in embryonic cardiac myocytes in vitro

The relationship of nascent myofibrils with the accumulation of adhesion plaque proteins and the formation of focal cell contacts was studied in embryonic chick cardiac myocytes in vitro. The cultures were double-stained with various combinations of the specific antiactin drug phalloidin and antibodies against vinculin, alpha-actinin, connectin (titin), myosin heavy chain, fibronectin, and desmin and examined under fluorescence and interference reflection microscopy. In the areas of myofibril assembly, vinculin and alpha-actinin plaques were formed at the ventral sarcolemmae. These areas overlapped with the sites of cell-to-substrate focal contacts and extracellular fibronectin. Because the myofibrils always ran in a straight line between these sites, polarized lines appeared to be generated within the cells in response to their physical (e.g., stress) and/or biochemical environment (e.g., adhesion plaque proteins). The possible presence of other factors cannot be ruled out for the proper alignment of myofibrils. As soon as myofibrils came to span between these adhesion sites, they exhibited typically mature cross-striated characteristics. Thus, the formation of these inferred lines has some relation to, or is in fact necessary for, the maturation of myofibrils, in addition to the directional arrangement of sarcomeric proteins. Additionally, synthesis and distribution of myosin and connectin were tightly linked during early developmental (premyofibril and myofibril) stages. The spatial deployment of desmin was not coupled with vinculin. Thus, connectin and desmin do not appear to form the initial scaffold of sarcomeres.

The surface morphology of the avian tectorial membrane

The structure of the tectorial membrane of the chick was evaluated by scanning electron microscopy (SEM), using standard techniques, and, for the first time, by studying unfixed tectorial membranes with video-enhanced light microscopy techniques (AVEC-DIC). The SEM pictures show a widely varying morphology, ranging from a fully perforated tectorial membrane to a completely closed upper boundary, with a smooth surface. Based on several indicators, it is concluded that the latter presents the more natural state. This was confirmed by the results of the AVEC-DIC technique, which show a highly homogeneous structure. In contrast to the bulk of the tectorial membrane, its lower surface shows discrete structures, especially regularly oriented fibril bundles.

Localization of pp60c-src in growth cone of PC12 cell

By immunocytochemical and biochemical techniques, we observed the localization and expression of pp60c-src in nerve growth factor (NGF)-treated PC12 cells. Immunostaining of pp60c-src is detected in the neuronal soma and the tips of neurites (growth cones). Immunofluorescence in the neurites is less significant. High-resolution microscopy reveals that the location of pp60c-src in growth cone is in good agreement with the adhesive site of growth cone to the substratum. The pp60c-src kinase activity and the pp60c-src protein level increase 3.1- to 3.5-fold and 2.0-fold during differentiation of PC12 cells, respectively. The pp60c-src levels in the neurite fraction are also higher than those in the neuronal soma fraction. These results support the immunocytochemical finding that pp60c-src is localized in growth cones of differentiated PC12 cells. Furthermore, we discuss the possible role of pp60c-src in growth cone.

Real-time observations of microtubule dynamic instability in living cells

Individual microtubule dynamics were observed in real time in primary cultures of newt lung epithelium using video-enhanced differential interference contrast microscopy and digital image processing. The linear filaments observed in cells corresponded to microtubules based on three criteria: (a) small particles translocated along them; (b) the majority of them disappeared after incubation in nocodazole; (c) and the distribution observed by differential interference contrast correlated with anti-tubulin immunofluorescence staining of the same cell. Microtubules were most clearly observed at the leading edge of cells located at the periphery of the epithelial sheet. Microtubules exhibited dynamic instability behavior: individual microtubules existed in persistent phases of elongation or rapid shortening. Microtubules elongated at a velocity of 7.2 micron/min +/- 0.3 SEM (n = 42) and rapidly shortened at a velocity of 17.3 micron/min +/- 0.7 SEM (n = 35). The transitions between elongation and rapid shortening occurred abruptly and stochastically with a transition frequency of 0.014 s-1 for catastrophe and 0.044 s-1 for rescue. Approximately 70% of the rapidly shortening microtubules were rescued and resumed elongation within the 35 x 35 micron microscopic field. A portion of the microtubule population appeared differentially stable and did not display any measurable elongation or shortening during 10-15-min observations.

Recognition and laboratory characteristics of an atypical oocyst of Cryptosporidium

Feces from some patients with clinically unremarkable cryptosporidiosis contained an unusual variety of oocyst not previously recognized. These atypical oocysts were shown by electron microscopy to have a distinctive three-layered outer coat and, by immunofluorescence with a monoclonal antiserum, to lack an antigen present on the surface of typical oocysts. In contrast to typical oocysts, the atypical variety is very fragile and quickly collapses when suspended in solutions of high osmotic pressure or in lipid solvents. Atypical oocysts cannot be stained by methods used to stain typical oocysts, but their appearance in sucrose-phenol is characteristic. Their stability in this solution, though much less than that of typical oocysts, is sufficient for them to be recognized and for cases to be diagnosed by microscopy. Patients who excreted atypical oocysts never excreted the typical variety. General findings in patients who excreted atypical oocysts were no different from those who excreted typical oocysts.

Fluorescent microtubules break up under illumination

We have synthesized three new fluorescent analogues of tubulin, using fluorescein or rhodamine groups attached to N-hydroxy-succinimidyl esters, and have partially characterized the properties of these analogues. We have also further characterized the tubulin derivatized with dichlorotriazinyl-aminofluorescein that has previously been used in this and other laboratories. Our results show that all four analogues assemble into microtubules which break up when exposed to light of the wavelengths that excite fluorescence. This sensitivity places severe constraints on the use of these analogues in studies of microtubule dynamics.

Micropruning: the mechanism of turning of Aplysia growth cones at substrate borders in vitro

Growth cones of Aplysia californica neurons were observed with video-enhanced contrast-differential interference contrast (VEC-DIC) microscopy as they turned at a border between poly-L-lysine-treated and untreated glass. Growth cones that turned generally developed 2 distinct active areas of filopodial and veil formation, much in the way of growth cones undergoing branching. Both active areas advanced, but turning of the neurite occurred through the selective resorption of the incipient branches developing on the untreated substrate. Thus, micropruning of developing regions of the growth cone, rather than the asymmetric extension of filopodia or veils, was primarily responsible for directing neurite growth. We present the hypothesis that abrupt turns by growing neurites are mediated by 2 sets of signals, one causing growth cone splitting, and a second set regulating the survival of the separate branches.

The organization of the cardiac ganglion of the axolotl (Ambystoma mexicanum)

The heart of the axolotl Ambystoma mexicanum was studied with histochemical methods to determine the distribution of neurons containing acetylcholine esterase, catecholamines and 5-hydroxytryptamine. The cardiac ganglion is made up of cholinergic nerve fibers and somata, and of catecholaminergic fibers. Small intensely fluorescent cells were found along blood vessels in the pericardial wall at the base of the heart, but not in the heart itself, except, in a few instances, in the region bordering the pericardial wall. Both the cholinergic and the catecholaminergic innervation of the heart were poorly developed at hatching and reached their mature state after a few months. Cholinesterase staining fibers appeared several weeks before catecholaminergic fibers. The number of postganglionic cholinergic neurons in the heart increased several-fold during the first month after hatching. Histofluorescence studies of organ cultures suggested that all the catecholamine present in the heart are of extrinsic origin. Liquid chromatography with electrochemical detection demonstrated that the dominant catecholamine in the heart is norepinephrine. No neurons containing 5-hydroxytryptamine were found.

The microtubule-dependent formation of a tubulovesicular network with characteristics of the ER from cultured cell extracts

The formation of a dynamic tubulovesicular membrane network that resembles the endoplasmic reticulum (ER) has been observed in extracts of cultured chick embryo fibroblasts (CEF cells) using video-enhanced differential interference contrast microscopy. Initially, membranes in the CEF extracts appeared amorphous and aggregated, but with time, membrane tubules moved out along stationary microtubules. The membrane tubules formed new branches on intersecting microtubules and fused with other branches to form a network of interconnected polygons. The tubulovesicular network was solubilized by detergent and took on a beaded morphology in a hypotonic buffer. Formation of the tubulovesicular network required ATP and microtubules. The network did not contain elements of the plasma membrane, Golgi apparatus, or mitochondria but could be labeled with ER markers. We suggest that the tubulovesicular network contains components from the ER and is formed by membrane associated motors moving upon microtubules in a process we call microtubule-dependent tethering.

Mutant expression of male copulatory bursa surface markers in Caenorhabditis elegans

In a search for molecular markers of male tail morphogenesis in C. elegans, we have detected two surface markers that are specifically observed in the copulatory bursa of adult males and the vulva of adult hermaphrodites. These markers are defined by binding of a monoclonal antibody (Ab117) and the lectin wheat germ agglutinin (WGA) to live intact animals. Expression of these markers is dependent on sex, stage and anterior-posterior position in the animal. Four of ten mutants with specific defects in bursal development show altered expression of one or both markers. Because the WGA marker can be expressed in intersexual animals with very little bursal development, posterior surface expression of this marker can serve as an indication of subtle masculinization of hermaphrodites. The timing of expression of these markers is not affected by heterochronic mutations that cause larval animals to express adult cuticles or adult animals to express larval cuticles, indicating that marker expression can be uncoupled from general cuticle development. Mutant lin-22 males, which have an anterior-to-posterior transformation of cell fates in the lateral hypodermis, ectopically express both markers in a manner consistent with a ‘posteriorization’ of positional information in these animals. These markers should be useful for the isolation and characterization of mutants defective in bursal and vulval development, sex determination and expression of anterior-posterior positional information.

Comparison of methods for the estimation of the thickness of ultrathin tissue sections

For a number of quantitative electron microscopical techniques it is relevant to obtain an estimate of the thickness t' of the section which, in general, will differ from the actual distance t between the two cuts that generate the section. To estimate t' of ultrathin sections, several techniques have been adopted in the past, both with and without the aid of the electron microscope and additional equipment, which are summarized in an appendix. In the present study five methods have been evaluated experimentally using sections of ten different interference colours: (a) the 'small-fold' technique, (b) the 'electron scattering' method, (c) interference microscopy with (A) the Vicker's M86 scanning microinterferometer and (B) the Jenoptik Amplival Interphako interference microscope and (d) the 're-embedding' method. Reliable, reproducible and comparable results were obtained with the small-fold technique, with the Vickers M86 scanning microinterferometer and with the electron scattering method. For the last method, standard test lines for the different settings of the electron microscope were developed. The results obtained with the Jenoptik Amplival Interphako interference microscope are reproducible, but show a constant difference, i.e. a factor of 1.36, in thickness compared with the other three techniques. The possible cause of this 'systematic error' is discussed. The re-embedding method proved to be more laborious and slightly less reliable than the other techniques. The variation in t' between sections of a particular interference colour (inter-section variation) was found to be larger than the variation in t' within a section (intra-section variation).

In vitro low frequency electromagnetic field effect on fast axonal transport

The objective of this study was to evaluate the effects of a low frequency electromagnetic field on fast axonal transport for future neuroprosthetic applications. Changes in speeds and densities of retrograde fast organelle transport in rat sciatic nerve preparations were measured in vitro upon exposure to 15 and 50 Hz pulsed magnetic fields with peak intensities of 4.4 and 8.8 mT. Maximum current density of the induced eddy current was calculated to be about 40 microA/cm2. Video enhanced differential interference contrast microscopy was used to record axons supporting active organelle transport. Strong effects were observed in myelinated axons (cessation of transport in up to 10 min). Such effects may eventually be used as part of a neuroprosthesis to noninvasively modify or couple to various parts of the nervous system.

Local role of Ca2+ in formation of veils in growth cones

A previous study that used high-resolution video (VEC-DIC) microscopy to examine axonal growth cones of Aplysia giant neurons growing in culture had demonstrated that growth occurs by the extension of veils of membrane between filopodia and the subsequent morphological transformation of these veils, in place, into the swollen, organelle-filled central region of the growth cone and then into the cylindrical axon. The possible involvement of Ca2+ in this sequence of events was now examined using VEC-DIC microscopy. Reduction of [Ca2+]o from the normal level of 11 to 1.3 mM or below or the addition of 20 mM Co2+, which blocks Ca2+ channels, caused a large decrease in the area of immature veil (flat and with few organelles) in the growth cone within minutes. Ba2+, 20 mM, which flows well through Ca2+ channels, and 5 microM A23187, a Ca2+ ionophore, caused new immature veil to form in the presence of reduced [Ca2+]o. Maturation of veil into central region was not inhibited by reduced [Ca2+]o. In fact, the disappearance of immature veil was often the result partly, or entirely, of continued veil maturation in the absence of formation of new veil. The next step in maturation, conversion of the central region to cylindrical axon, was also probably not inhibited by reduced [Ca2+]o. Ca2+ was microapplied to large growth cones that had lost their veils by exposure to reduced [Ca2+]o. There was a strong tendency for the first, or only, incidence of veil formation to occur near the micropipette, the rest of the perimeter of the growth cone remaining quiescent. It is concluded that intracellular Ca2+ plays a role in veil formation and that the site of the Ca2+-dependent step is close to the site of veil formation. If this step is exocytosis, veil forms where there is net addition of membrane. Whether a change in [Ca2+]i, rather than some other factor, normally directly triggers veil formation remains uncertain, but, if it does, then the site of formation, which will strongly influence the direction of axon growth, is probably determined by focal changes in [Ca2+]i within the growth cone.

A comparison of Giardia microti and Spironucleus muris cysts in the vole: an immunocytochemical, light, and electron microscopic study

We have shown that cysts of the genus Spironucleus share many common morphological features with Giardia cysts including: 2-4 nuclei, flagellar axonemes, a distinct cyst wall, and they even display the same immunostaining as Giardia cysts when labeled with antibodies specific for Giardia cyst wall. A direct comparison of Spironucleus muris and Giardia microti cysts have revealed that cysts of S. muris are significantly smaller than cysts of G. miroti. At the ultrastructural level, the cyst walls are similar in fibrillar appearance, but the width of the S. muris cyst wall is significantly less than that of G. microti. The cysts of S. muris also differ from G. microti in that they contain a striated rootlet fiber, flagellar sheath, and numerous glycogen rosettes. Characteristic features of Giardia include the adhesive disc and median body. Although the cysts of Spironucleus and Giardia are similar in appearance, these unique morphological features can be used to distinguish between the 2 protozoa and should be employed in the detection of Giardia cysts in water samples.

Contacts of chick fibroblasts on glass: results and limitations of quantitative interferometry

We have examined the contacts made by explanted chick heart and limb bud fibroblasts after 24–48 h on glass, using quantitative interference reflection microscopy (IRM). Contacts beneath very thin cytoplasmic lamellae were avoided because the images of such contacts depend on the thickness of the lamellae. Plaque-like focal contacts, distinguished on the basis of shape and low irradiance (darkness), are intimate adhesions to the substratum. These images can be interpreted if it is assumed that microfilaments associated with the lower membrane increase the local cytoplasmic refractive index. The range of irradiances measured for focal contacts was found to be rather wide, and our modelling shows that the most likely explanation for this is that the images receive variable contributions from the adjacent cytoskeleton. For this reason it is particularly difficult to assign a characteristic thickness for these contacts from IRM data. Close contacts, seen principally as ‘grey’ regions under migrating cells at the edges of the explants, also show a wide range of irradiances. Unlike focal contacts, it is not necessary to postulate any involvement of the cytoskeleton in their images and they can be modelled as regions where an aqueous glycocalyx zone about 20–30 nm thick separates the membrane bilayer from the glass. Paler grey regions that also look like close contacts are apparently formed where the cell surface has lifted several tens of nanometres from the glass.

Attachment of Pseudomonas fluorescens to glass and influence of electrolytes on bacterium-substratum separation distance

The influence of Na+, Ca2+, La3+, and Fe3+ on the adhesion of Pseudomonas fluorescens H2 and H2S was investigated with interference reflection microscopy (IRM). IRM is a light microscopy technique which allows (i) visualization of the adhesive sites of living bacteria as they attach to a glass cover slip surface and (ii) evaluation of the bacterium-glass surface separation distance within a range of 0 to ca. 100 nm. The addition of each cation caused changes in IRM images consistent with a decrease in the separation distance, and minimum effective concentrations were as follows: Na+, 1 mM; Ca2+, 1 mM; La3+, 50 microM; and Fe3+, 50 microM. With strain H2, the effects of Na+, Ca2+, and La3+ were fully reversible in that the separation distance increased again when the electrolyte was replaced with distilled water. However, with strain H2S, a spontaneous mutant of H2 with increased attachment ability, only the effect of Na+ was fully reversible, and the effects of Ca2+ and La3+ were only partially reversible or irreversible. The effect of Fe3+ was irreversible with both strains, but this may be related not only to the electrolytic nature of Fe3+ but also to the decrease in solution pH to 3.5 caused by its addition. It is proposed that the electrolytes caused a decrease in separation distance by neutralizing negative charges on bacterial surface polymers and that the different effects obtained with the two strains are related to their different adhesion abilities.

Differential response to compressive loads of zones of canine hyaline articular cartilage: micromechanical, light and electron microscopic studies

Thin (100 micron) perpendicular slices of canine femoral condylar cartilage were placed horizontally on the stage of a Nachet microscope and viewed by transmitted light in the differential interference contrast mode. Each slice was held on the microscope stage by a loading rig and tested mechanically in compression. Measured loads to a maximum of approximately 2-3 MN/m2 were applied to the end of the slice corresponding to the articular surface. Photographs were taken of the cartilage before and during loading, and the distance by which selected chondrocytes were displaced was used as an index of mechanical strain, i.e., of change in length/original length. Maximum strains were observed in the superficial cartilage zone. Minimum strains were recorded in the mid-zone, at a depth corresponding to approximately 75% of the total cartilage thickness. The relative concentrations of cartilage collagen (COL) and proteoglycan (PG) were assessed by the light and electron microscopic histochemical study of cartilage sections taken from contiguous blocks. Superficial cartilage, which deformed most, had high concentrations of oriented COL fibres, low concentrations of PG. Mid-zone cartilage, which deformed least, had lower concentrations of randomly arrayed COL fibres but relatively high concentrations of PG.

Observation of two structures of the tear film lipid layer

The behaviour of the tear film exposed to the atmosphere for a relatively long time was observed by means of a Nomarski microscope and the Zeiss slit-lamp microscope SL 75. It was observed that the lipid layer of the tear film on the naked eye as well as over the contact lens consists of two structures: the homogeneous structure and a structure exhibiting a micelle-like one. The phenomenon is explained in terms of the specific properties of the different lipids in the gland secretions.

[Formation of an actin cytoskeleton and adhesive structures during the spreading of cultured cells]

Fibroblast spreading was studied using immunofluorescent method that provided visualization of actin structures and adhesion contacts in the same cell. Four stages of actin system formation were observed. 1. Actin concentration in ruffles at the cell periphery. Formation of numerous dot-like contacts along the whole perimeter of the cell. 2. Formation of a circumferential actin bundle. Focal contacts are located at the outer edge of the bundle. 3. Gradual transformation of the circumferential bundle into actin network with triangular meshes. Peripheral (rather than internal) filaments of the network are associated with the focal contacts. 4. Appearance of the system of long straight actin bundles (stress fibers) associated with dash-like focal contacts. The stress fibers are supposed to arise from the triangular actin network which in its turn arises from the circumferential bundle. It is suggested that the formation of actin cytoskeleton is a process driven by the development of tensions in actin structures attached to the focal contacts at the cell periphery.