A distributed model of exchange processes within the osteon.

In order to understand various exchange processes within the osteon, a mathematical model to describe the system has been developed which allows for concentration gradients in the axial and radial directions as well as cellular consumption and binding to bone surface. The normal values for the model parameter are discussed and the effects of the model parameters on the behaviour of the model are investigated. This model supports the idea that diffusion alone may be an inefficient mechanism in transport between blood and osteocytes.     

Maturing of fibrils and intraosseous osteogenesis as a basis for the development of lamellae and the osteon structure]

We investigated in continuation of lightmicroscopical (phasecontrast, polarized light) and statistical studies concerning the formation of lamellae and osteons electromicroscopical the nature of fibrils in different areas of the cross section of the metacarpus from a cattle fetus of 520 mm SSL. During the maturation of fibrils in a subperiostal trabecal the diameter of fibrils increased (465 to 470 A). The period (316 or 536 A) contains primarily only a broad band and a small interband. Subsequently the interband increased (221 or 215 A), but the band decreased (324 or 271 A). In the centre of trabeculae the fibrils formate microlamellae. The fibrils split later on in the medial part of the cross section in microfibrils with irregular oreintation and appear lightmicroscopical as intermediate tissue (blasse Mittellinie). At the same time new fibrils are synthesized around the osteocytes and their canaliculi. As the result of a kind of remodeling the fibrils arrange in a parallel order forming packages which appear lightmicroscopical as fibrous felts. These fibrous felts exhibits partly an periodical arrangement with a small band (164 A) and a wide interband (287 A). In a following stage in the fibrous felts lamellae are developed, the length of which increased around the medullary cavity. Firstly after the development of lamellae the definite bone fibrils are reconstituted (diameter: 530 A; band: 348 A; interband: 212 A). Apparently the osteocytes are responsible for these procedures in a stage specific synthetic and lytic activity. The modification of the nature of fibrils results probably after the dissolving of the structural glycoproteins, which stabilize the tropocollagen molecules. A reconstitution of the structural glycoproteins after formation of the lamellae induce the reconstitution of bone specific collagenfibrils. The regulating mechanism for the codification of these structural development are unknown.     

An estimate of anisotropic poroelastic constants of an osteon

The anisotropic poroelastic constants of an osteon are estimated by micromechanical analysis. Two extreme cases are examined, the drained and the undrained elastic constants. The drained elastic constants are the porous medium’s effective elastic constants when the fluid in the pores easily escapes and the pore fluid can sustain no pore pressure. The undrained elastic constants are the porous medium’s effective elastic constants when the medium is fully saturated with pore fluid and the fluid cannot escape. The drained and undrained elastic constants at the lacunar and canalicular porosity tissue levels are estimated by using an effective moduli model consisting of the periodic distribution of ellipsoidal cavities. These estimated anisotropic poroelastic constants provide a database for the development of an accurate anisotropic poroelastic model of an osteon.     

Motion of particles adhering to the leading lamella of crawling cells

Time-lapsed films of particle motion on the leading lamella of chick heart fibroblasts and mouse peritoneal macrophages were analyzed. The particles were composed of powdered glass or powdered aminated polystyrene and were 0.5-1.0 micrometer in radius. Particle motions were described by steps in position from one frame to the time-lapse movies to the next. The statistics of the step-size distribution of the particles were consistent with a particle in Brownian motion subject to a constant force. From the Brownian movement, we have calculated the two-dimensional diffusion coefficient of different particles. These vary by more than an order of magnitude (10(-11)-10(-10) cm2/s) even for particles composed of the same material and located very close to each other on the surface of the cell. This variation was not correlated with particle size but is interpretable as a result of different numbers of adhesive bonds holding the particles to the cells. The constant component of particle movement can be interpreted as a result of a constant force acting on each particle (0.1-1.0 x 10(-8) dyn). Variations in the fractional coefficient for particles close to each other on the cell surface do not yield corresponding differences in velocity, suggesting that the frictional coefficient and the driving force vary together. This is consistent with the hypothesis that the particles are carried by flow of the membrane as a whole or by flow of some submembrane material. The utility of our methods for monitoring cell motile behavior in biologically interesting situations, such as a chemotactic gradient, is discussed.     

Patterns of chemical diversity in the Mediterranean sponge Spongia lamella

The intra-specific diversity in secondary metabolites can provide crucial information for understanding species ecology and evolution but has received limited attention in marine chemical ecology. The complex nature of diversity is partially responsible for the lack of studies, which often target a narrow number of major compounds. Here, we investigated the intra-specific chemical diversity of the Mediterranean sponge Spongia lamella. The chemical profiles of seven populations spreading over 1200 km in the Western Mediterranean were obtained by a straightforward SPE-HPLC-DAD-ELSD process whereas the identity of compounds was assessed by comparison between HPLC-MS spectra and literature data. Chemical diversity calculated by richness and Shannon indexes differed significantly between sponge populations but not at a larger regional scale. We used factor analysis, analysis of variance, and regression analysis to examine the chemical variability of this sponge at local and regional scales, to establish general patterns of variation in chemical diversity. The abundance of some metabolites varied significantly between sponge populations. Despite these significant differences between populations, we found a clear pattern of increasing chemical dissimilarity with increasing geographic distance. Additional large spatial scale studies on the chemical diversity of marine organisms will validate the universality or exclusivity of this pattern.     

A discrete model for streaming potentials in a single osteon

A mathematical model for streaming potentials in an osteon is proposed, taking into account the microstresses in the vicinity of the Haversian Canal. With the help of the finite element method, a boundary problem for the fluid pressure amplitude in the osteon is investigated when the bone sample is subjected to harmonic loading. A numerical analysis of the intra-osteonal potential is performed. It is found that there exists an azimuthal asymmetry which increases with the enlargement of the Haversian Canal. The results of the numerical modeling of the intra-osteonal potential are in accordance with the available experimental data.     

Modeling of bone at a single lamella level

This paper focuses on the ultrastructure of bone at a single lamella level. At this scale, collagen fibrils reinforced with apatite crystals are aligned preferentially to form a lamella. At the next structural level, such lamella are stacked in different orientations to form either osteons in cortical bone or trabecular pockets in trabecular bone. We use a finite element model, which treats small strain elasticity of a spatially random network of collagen fibrils, and compute anisotropic effective stiffness tensors and deformations of such a single lamella as a function of fibril volume fractions (or porosities), prescribed microgeometries, and fibril geometric and elastic properties.     

Ultrastructure of the secondary gill lamella of the icefish, Chaenocephalus aceratus

The basic structure of the secondary lamella is similar to that found in most fishes, but the water/blood barrier is relatively thick (c. 8 pm) of which about 90% is epithelium. The marginal channel is larger than channels between pillar cells which appear to have contracted.     

Structure of the antineoplastic antibiotic variamycin]

The results of the structural study of antitumor antibiotic variamycin and its peracetyl derivative by 1H-and 13C-NMR spectroscopy are reported. Structures of carbohydrate chains of the antibiotics molecule are revised. Variamycin is shown to be 2-[beta-cymmarosyl(1-3)-beta-oliosyl (1-3)-beta-olivosyl]-6-[beta-olivosyl (1-3)-beta-olivosyl] chromomycinone.     

Structure of the mRNA of eukaryotic cells]

A review is given of the principal achievements in studying the structure of mRNA in eukaryotic cells. The data are provided on the size and life time, complexity and distribution of different kinds of mRNA by the frequency of repetitions; composition and structure of mRNP. The structures of individual mRNA's and general pattern of the structure of eukaryotic mRNA and mRNP are considered.     

Macrophage podosomes assemble at the leading lamella by growth and fragmentation

Podosomes are actin- and fimbrin-containing adhesions at the leading edge of macrophages. In cells transfected with beta-actin-ECFP and L-fimbrin-EYFP, quantitative four-dimensional microscopy of podosome assembly shows that new adhesions arise at the cell periphery by one of two mechanisms; de novo podosome assembly, or fission of a precursor podosome into daughter podosomes. The large podosome cluster precursor also appears to be an adhesion structure; it contains actin, fimbrin, integrin, and is in close apposition to the substratum. Microtubule inhibitors paclitaxel and demecolcine inhibit the turnover and polarized formation of podosomes, but not the turnover rate of actin in these structures. Because daughter podosomes and podosome cluster precursors are preferentially located at the leading edge, they may play a critical role in continually generating new sites of cell adhesion.     

Preferential attachment of membrane glycoproteins to the cytoskeleton at the leading edge of lamella

The active forward movement of cells is often associated with the rearward transport of particles over the surfaces of their lamellae. Unlike the rest of the lamella, we found that the leading edge (within 0.5 microns of the cell boundary) is specialized for rearward transport of membrane-bound particles, such as Con A-coated latex microspheres. Using a single-beam optical gradient trap (optical tweezers) to apply restraining forces to particles, we can capture, move and release particles at will. When first bound on the central lamellar surface, Con A-coated particles would diffuse randomly; when such bound particles were brought to the leading edge of the lamella with the optical tweezers, they were often transported rearward. As in our previous studies, particle transport occurred with a concurrent decrease in apparent diffusion coefficient, consistent with attachment to the cytoskeleton. For particles at the leading edge of the lamella, weak attachment to the cytoskeleton and transport occurred with a half-time of 3 s; equivalent particles elsewhere on the lamella showed no detectable attachment when monitored for several minutes. Particles held on the cell surface by the laser trap attached more strongly to the cytoskeleton with time. These particles could escape a trapping force of 0.7 X 10(-6) dyne after 18 +/- 14 (sd) s at the leading edge, and after 64 +/- 34 (SD) s elsewhere on the lamella. Fluorescent succinylated Con A staining showed no corresponding concentration of general glycoproteins at the leading edge, but cytochalasin D-resistant filamentous actin was found at the leading edge. Our results have implications for cell motility: if the forces used for rearward particle transport were applied to a rigid substratum, cells would move forward. Such a mechanism would be most efficient if the leading edge of the cell contained preferential sites for attachment and transport.     

Structure of the perineurium of the peripheral nervous system]

The structure of the perineurium in different parts of the peripheral nervous system of rats, rabbits and cats was studied by light-optical and electron microscopic methods. The structure of the perineurium in all the animals studied is sim8lar and consists of different number of the epithelial type layers of the perineural cells, with bundles of cooagnous fibres between them. The greatest anount of layers is found in the perineurium of the sensory and vegetative ganglia, their amount being less between the nerve trunks and bundles. Solitary sensory mielinated nerve fibres are surrounded with a perineural etui consisting of one or two cellular layers. The thickness of the perineural cells varies from 300 to 1500 A and only in the nucleus field it is equal to 1-2 mu. Every layer of the perineural cells is surrounded by a basal membrane. In their cytoplasm there are many pinocytic vesicles in addition to main organells. Between the perineural cells there exist close contacts. The internal layer of the perineurium is the place of origin of intraganglionic septa and in certain distance surrounds the vessels entering the ganglion. Ultrastructurally the perineural cells are similar to the endothelium of the vessels.     

The estimated elastic constants for a single bone osteonal lamella

Micromechanical estimates of the elastic constants for a single bone osteonal lamella and its substructures are reported. These estimates of elastic constants are accomplished at three distinct and organized hierarchical levels, that of a mineralized collagen fibril, a collagen fiber, and a single lamella. The smallest collagen structure is the collagen fibril whose diameter is the order of 20 nm. The next structural level is the collagen fiber with a diameter of the order of 80 nm. A lamella is a laminate structure, composed of multiple collagen fibers with embedded minerals and consists of several laminates. The thickness of one laminate in the lamella is approximately 130 nm. All collagen fibers in a laminate in the lamella are oriented in one direction. However, the laminates rotate relative to the adjacent laminates. In this work, all collagen fibers in a lamella are assumed to be aligned in the longitudinal direction. This kind of bone with all collagen fibers aligned in one direction is called a parallel fibered bone. The effective elastic constants for a parallel fibered bone are estimated by assuming periodic substructures. These results provide a database for estimating the anisotropic poroelastic constants of an osteon and also provide a database for building mathematical or computational models in bone micromechanics, such as bone damage mechanics and bone poroelasticity.