Search PubMed⌕ Search

Biomedical subjects

T Volk

Publications and source records attributed to T Volk.

88 records · Page 5Linked to original sources
PubMed1987

Formation of heterotypic adherens-type junctions between L-CAM-containing liver cells and A-CAM-containing lens cells.

Cultured cells from either chicken lens or liver plated on solid substrates form flat epithelial sheets with adherens-type junctions between them. In lens cells these junctions contain A-CAM, while the same type of intercellular junctions in liver cells contain another cell adhesion molecule, L-CAM. Coculturing of lens and liver cells in the same dish resulted in the formation of mixed (heterotypic) adherens junctions. Double immunofluorescent labeling for both A-CAM and L-CAM indicated that the mixed junctions contained both molecules, each of which was present on one of the two partner cells. Moreover, the formation of the heterotypic junctions could be effectively inhibited by both anti-A-CAM and anti-L-CAM antibodies. It has thus been proposed that A-CAM and L-CAM share significant functional homology and may be involved in heterophilic interactions leading to the establishment of molecularly and cellularly asymmetrical adherens-type junctions.

Animals↗
PubMed1987

A modular BLSS simulation model.

The coordination of material flows in Earth's biosphere is largely made possible by the buffering effect of huge material reservoirs. Without similarly-sized buffers, a bioregenerative life support system (BLSS) for extraterrestrial use will be faced with coordination problems more acute than those in any ecosystem found on earth. A related problem is BLSS design is providing an interface between the various life-support processors, one that will allow for their coordination while still allowing for system expansion. Here we present a modular model of a BLSS that interfaces system processors only with the material storage reservoirs, allowing those reservoirs to act as the principal buffers in the system and thus minimizing difficulties with processor coordination. The modular nature of the model allows independent development of the detailed submodels that exist within the model framework. Using this model, BLSS dynamics were investigated under normal conditions and under various failure modes. Partial and complete failures of various components, such as the waste processor or the plants themselves, drive transient responses in the model system, allowing us to examine the effectiveness of the system reservoirs as buffers. The results from simulations of this sort will help to determine control strategies and BLSS design requirements. An evolved version of this model could be used as an interactive control aid in a future BLSS.

Computer Simulation↗
PubMed1987

Mass balances for a biological life support system simulation model.

Design decisions to aid the development of future space-based biological life support systems (BLSS) can be made with simulation models. Here we develop the biochemical stoichiometry for 1) protein, carbohydrate, fat, fiber, and lignin production in the edible and inedible parts of plants; 2) food consumption and production of organic solids in urine, feces, and wash water by the humans; and 3) operation of the waste processor. Flux values for all components are derived for a steady-state system with wheat as the sole food source. The large-scale dynamics of a materially-closed (BLSS) computer model is described in a companion paper. An extension of this methodology can explore multi-food systems and more complex biochemical dynamics while maintaining whole-system closure as a focus.

Biomass↗
PubMed1987

Molecular interactions in adherens-type contacts.

Adherens junctions are members of a molecularly and structurally heterogeneous family of cell contacts sharing a common association with the microfilament system. Various topics related to the biogenesis of these cellular contacts and the molecular interactions involved in their formation are discussed. The role of vinculin, a cytoplasmic 'plaque' component present in all adherens junctions tested to date and its possible interactions with the other junctional domains have been investigated by both biochemical analyses and studies of molecular dynamics in microinjected living cells. The importance of A-CAM, which apparently functions as a 'junctional receptor' is emphasized and its roles in junction formation in cell cultures and in developing embryos are discussed. In addition, its relationship to other Ca2+-dependent cell adhesion molecules (in particular L-CAM) is considered. The evidence indicating that the level of expression of vinculin-specific mRNA is affected by culture conditions and may be markedly modulated by changes in the adhesiveness of the substratum on which the cells grow is reviewed.

Animals↗
PubMed1986

A-CAM: a 135-kD receptor of intercellular adherens junctions. I. Immunoelectron microscopic localization and biochemical studies.

The recently described adherens junction-specific 135-kD protein (Volk, T., and B. Geiger, 1984, EMBO (Eur. Mol. Biol. Organ.) J., 3:2249-2260) was localized along cardiac muscle intercalated discs by immunogold labeling of ultrathin frozen sections. Analysis of this labeling indicated that the 135-kD protein, adherens junction-specific cell adhesion molecule (A-CAM), is tightly associated with the plasma membrane unlike vinculin labeling, which was present along the membrane-bound plaques of the fascia adherens. In cultured chick lens cells, A-CAM was associated with Ca2+-dependent junctions that were cleaved upon a decrease of extracellular Ca2+ concentrations to less than or equal to 0.5 mM. In the chelator-separated junction, A-CAM became exposed to exogenously added antibodies or to proteolytic enzymes. Upon addition of trypsin to EGTA-treated cells, A-CAM was cleaved into three major cell-bound antigenic peptides with apparent molecular masses of 78, 60, and 46 kD, suggesting that the extracellular domain of A-CAM has a size greater than or equal to kD. Incubation of electrophoretic gels with 125I-concanavalin A (Con A) indicated that one of the major Con A-binding proteins in chicken lens membranes is a integral of 135-kD glycoprotein that was partially purified on Con A-Sepharose column and identified as A-CAM by immunoblotting. Detergent partitioning assay using Triton X-114 biphasic system was carried out to determine whether A-CAM displays properties of an integral membrane protein. This assay indicated that the intact A-CAM molecule was recovered in the buffer phase but its cell-associated tryptic peptides, which presumably lost a great part of the A-CAM extracellular extension, readily partitioned into the detergent phase. The results obtained in this and in the following paper (Volk, T., and B. Geiger, 1986, J. Cell Biol., 103:1451-1464) strongly suggest that A-CAM is a Ca2+-dependent adherens junction-specific membrane glycoprotein that is involved in intercellular adhesion in these sites.

Animals↗
PubMed1986

A-CAM: a 135-kD receptor of intercellular adherens junctions. II. Antibody-mediated modulation of junction formation.

Intercellular adherens junctions between cultured lens epithelial cells are highly Ca2+-dependent and are readily dissociated upon chelation of extracellular Ca2+ ions. Addition of Ca2+ to EGTA-treated cells results in the recovery of cell-cell junctions including the reorganization of adherens junction-specific cell adhesion molecule (A-CAM), vinculin, and actin (Volk, T., and B. Geiger, 1986, J. Cell Biol., 103:000-000). Incubation of cells during the recovery phase with Fab' fragments of anti-A-CAM specifically inhibited the re-formation of cell-cell adherens junctions. This inhibition was accompanied by remarkable changes in microfilament organization manifested by an apparent deterioration of stress fibers and the appearance of fragmented actin bundles throughout the cytoplasm. Incubation of EGTA-dissociated cells with intact divalent anti-A-CAM antibodies in normal medium had no apparent inhibitory effect on junction formation and did not affect the assembly of actin microfilament bundles. Moreover, adherens junctions formed in the presence of the divalent antibodies became essentially Ca2+-independent, suggesting that cell-cell adhesion between them was primarily mediated by the antibodies. These studies suggest that A-CAM participates in intercellular adhesion in adherens-type junctions and point to its involvement in microfilament bundle assembly.

Actin Cytoskeleton↗
PubMed1985

Molecular heterogeneity of adherens junctions.

We describe here the subcellular distributions of three junctional proteins in different adherens-type contacts. The proteins examined include vinculin, talin, and a recently described 135-kD protein (Volk, T., and B. Geiger, 1984, EMBO (Eur. Mol. Biol. Organ.) J., 10:2249-2260). Immunofluorescent localization of the three proteins indicated that while vinculin was ubiquitously present in all adherens junctions, the other two showed selective and mutually exclusive association with either cell-substrate or cell-cell adhesions. Talin was abundant in focal contacts and in dense plaques of smooth muscle, but was essentially absent from intercellular junctions such as intercalated disks or adherens junctions of lens fibers. The 135-kD protein, on the other hand, was present in the latter two loci and was apparently absent from membrane-bound plaques of gizzard or from focal contacts. Radioimmunoassay of tissue extracts and immunolabeling of cultured chick lens cells indicated that the selective presence of talin and of the 135-kD protein in different cell contacts is spatially regulated within individual cells. On the basis of these findings it was concluded that adherens junctions are molecularly heterogeneous and consist of at least two major subgroups. Contacts with noncellular substrates contain talin and vinculin but not the 135-kD protein, whereas their intercellular counterparts contain the latter two proteins and are devoid of talin. The significance of these results and their possible relationships to contact-induced regulation of cell behavior are discussed.

Animals↗
PubMed1984

A 135-kd membrane protein of intercellular adherens junctions.

We report here on a new 135-kd membrane protein which is specifically associated with intercellular adherens-type junctions. This surface component was identified by a monoclonal antibody, ID-7.2.3, raised against detergent-extracted components of membranes of chicken cardiac muscle rich in intercalated discs. The antibodies stain extensively adherens junctions in intact cardiac muscle and in lens, as well as in cultured cells derived from these tissues. In living cultured cells only very little immunolabelling was obtained with ID-7.2.3 antibodies, probably due to the limited accessibility of the antibodies to the intercellular gap. However, upon the removal of extracellular Ca2+ ions a dissociation of the junction occurred, leading to the rapid exposure of the 135-kd protein. Immunoelectron microscopic labelling of EGTA-treated, or detergent-permeabilized cells indicated that the antigen is found along the plasma membrane and highly enriched in contact areas. Double immunolabelling for both the 135-kd protein and vinculin pointed to the close association of the two in intercellular junctions and to the apparent absence of the former protein from the vinculin-rich focal contacts of cultured cells and from dense plaque of smooth muscle. Immunoblotting indicated that the 135-kd protein is present in many tissues but is particularly enriched in heart, lens and brain.

Animals↗
PubMed1984

Motility and adhesive properties of high- and low-metastatic murine neoplastic cells.

Randomly chosen clones of the murine K-1735 melanoma tumor were used by Raz and Geiger to address the question of whether variations in actin organization in these cells may be related to their lung colonization capability in syngeneic hosts (Cancer Res., 42: 5183-5190, 1982). In 14 of 15 clones tested, we found that the degree of actin organization was inversely correlated to their metastatic capability. We have further shown that remarkable variations exist in the adhesive properties and locomotor activity of four K-1735 melanoma cell variants that exhibit distinct metastatic properties. The low-metastatic cell variants displayed large focal adhesion plaques, tightly packed actin bundles, elaborate extracellular networks of fibronectin, and restricted motility. In contrast, the high-metastatic variants were poorly attached with only few distinct actin bundles, were unable to reorganize extracellular fibronectin into cables, and exhibited high motile activity. Electron microscopic examination of local s.c. tumors of the high- and low-metastatic lines indicated that the former formed loose tumor masses with very few intercellular connections, while the low-metastatic line developed into a considerably more compact tumor with numerous intercellular contacts, in line with the in vitro findings. It is proposed that the differences in cellular properties manifested by these cell lines may be related to their metastatic properties. Specifically, the highly metastatic cells of this tumor system may easily detach from the primary tumor mass, form weak and transient connections with surrounding connective tissue, and actively migrate through it. Furthermore, these results point to the close interrelationships between different mechanochemical features in cells, including specific cell adhesiveness, cytoskeletal organization, locomotion, and rearrangement of extracellular fibronectin. The possible nature of these interrelationships is discussed.

Actins↗
PubMed1983

On spatial periodicity in the formation of cell adhesions to a substrate.

Interference reflection microscopy reveals a fairly regular array of marginal focal contacts in early states of cell spreading. A theoretical explanation of the onset of patchiness is given, based on the positively cooperative binding to the substrate of laterally diffusing receptor molecules.

Animals↗
PubMed1976

Studies on new process procedures in plasma fractionation on an industrial scale. I. Determination of the pH value of ethanol containing protein solutions at low temperatures.

A suitable combined pH electode is evaluated which provides reproducible readings under the extreme conditions of the cold ethanol plasma fractionation procedure. Adequately reproducible correlations are found between the pH measurements in protein solutions with an ethanol content of up to 40% at temperatures as low as -8 degrees C and the determination in diluted samples at room temperature using the standard procedure.

Chemical Fractionation↗
PubMed1976

Studies on new process procedures in plasma fractionation on an industrial scale. II. Experiments in concentrating dilute albumin solutions using hollow fiber ultrafiltration.

Ultrafiltration with a hollow fiber device was studied as an alternative method to the lyophilization or thin-layer distillation techniques in the production of salt-poor, concentrated human albumin preparations for clinical use. A number of process parameters are discussed. Combination of gel filtration and ultrafiltration provides an interesting alternative to the currently used systems.

Chemical Fractionation↗
PubMedDate not supplied

[Use of peridural catheters in the treatment of postoperative pain after spinal instrumentated fusion--an experience report].

AIM: In a prospective randomized clinical study we investigated in a group of 20 patients after spinal instrumentation surgery the analgesic efficacy and the safety of epidural analgesia. Intraoperatively an epidural catheter was placed by the orthopedic surgeons for postoperative pain control. METHOD: For epidural catheter analgesia a mixture of the local anesthetic ropivacaine and the opioid sufentanil was used with an initial bolus, followed by a continuous infusion and the possibility of patient-controlled bolus administration (PCEA). Pain-scores (VAS) were measured pre- and postoperatively at rest, and during active mobilization maneuvers like turning around in bed and standing. The neurological status, side effects, and complications were evaluated. RESULTS: Mean pain-scores (VAS) were 3.8 pre-operatively at rest, after initiation of epidural analgesia 0.3 at rest, 1.6 at turning around in bed and 0.8 at standing (6.8 pre-operatively). Transient sensible or motoric deficits, due to the local anesthetics' effect, occurred in 8 respectively in 3 of the patients. Drug-induced typical side-effects were pruritus, nausea and emesis. No cardiopulmonary complications happened. CONCLUSION: The epidural lumbal analgesia is an effective and safe method to control postoperative pain after spinal instrumentation surgery. Precondition is the knowledge about the safe and standardized technique of intraoperative catheter placement by the orthopedic surgeon, the choice of the appropriate analgesic drugs and a good cooperation between the departments of anesthesiology and orthopedic surgery and nursing staff.

Adult↗
PubMedDate not supplied

The influence of cellular hypoxia and reactive oxygen species on the development of endothelial cell edema.

We investigated in vitro whether endothelial cell edema is induced by cellular hypoxia or oxygen radical formation. Measurements of relative cell volume (RCV) were made using microweight analysis, liquid scintillation spectrometry and analysis of cellular protein content. To validate this method of determining cell volume, endothelial cells were incubated in media of different osmolarities. Vascular endothelial cells reacted to osmotic stress with a volume increase or decrease. The addition of xanthine oxidase (XOD; 3 mU/ml) and hypoxanthine (1 mM) for the enzymatic production of O2- caused a reproducible and significant increase in RCV by 29 +/- 8% (from 5.5 to 7.1 microliters/10(6) cells; p < 0.001) after an incubation time of 60 min. Nonenzymatically produced H2O2 (100 microM) caused a similar increase in RCV by 35 +/- 5% (from 5.5 to 7.6 microliters/10(6) cells; p < 0.001) over the same incubation period. The addition of catalase (50 U/ml) diminished the increasing effect of XOD as well as that of H2O2 on cell volume. As assessed by the uptake of the vital dye trypan blue and the release of lactate dehydrogenase into the medium, there was no significant loss of viability during the incubation time. Lower concentrations of H2O2 as well as lower activities of XOD did not induce a significant increase in RCV. Higher H2O2 concentrations and increased XOD activities caused a considerable time- and concentration-dependent injury of endothelial cells. RCV was unchanged even after long exposure (5 h) to two different hypoxic gas mixtures (3% O2:5% CO2:92% N2; 0% O2:5% CO2:95% N2). Cell viability was not impaired under hypoxic conditions. The results suggest that reactive oxygen species play a more important role in the development of endothelial cell edema than cellular hypoxia.

Animals↗
PubMedDate not supplied

Modeling light and temperature effects on leaf emergence in wheat and barley.

Phenological development affects canopy structure, radiation interception, and dry matter production; most crop simulation models therefore incorporate leaf emergence rate as a basic parameter. A recent study examined leaf emergence rate as a function of temperature and daylength among wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) cultivars. Leaf emergence rate and phyllochron were modeled as functions of temperature alone, daylength alone, and the interaction between temperature and daylength. The resulting equations contained an unwieldy number of constants. Here we simplify by reducing the constants by > 70%, and show leaf emergence rate as a single response surface with temperature and daylength. In addition, we incorporate the effect of photosynthetic photon flux into the model. Generic fits for wheat and barley show cultivar differences less than +/- 5% for wheat and less than +/- 10% for barley. Barley is more sensitive to daylength changes than wheat for common environmental values of daylength, which may be related to the difference in sensitivity to daylength between spring and winter cultivars. Differences in leaf emergence rate between cultivars can be incorporated into the model by means of a single, nondimensional factor for each cultivar.

Hordeum↗