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A S Curtis

Publications and source records attributed to A S Curtis.

At least 37 records · Page 2Linked to original sources
PubMed1990

An extracellular microelectrode array for monitoring electrogenic cells in culture.

This paper describes a planar array of microelectrodes developed for monitoring the electrical activity of cells in culture. The device allows the incorporation of surface topographical features in an insulating layer above the electrodes. Semiconductor technology is employed for the fabrication of the gold electrodes and for the deposition and patterning of an insulating layer of silicon nitride. The electrodes have been tested using a cardiac cell culture of chick embryo myocytes, and the physical beating of the cultured cells correlated with the simultaneous extracellular voltage measurements obtained. It was found that extracellular stimulation of the cells was possible via the same electrodes used for recording.

Action Potentials↗
PubMed1990

Topographical control of cell behaviour: II. Multiple grooved substrata.

Electronics miniaturization techniques have been used to fabricate substrata to study contact guidance of cells. Topographical guidance of three cell types (BHK, MDCK and chick embryo cerebral neurones) was examined on grooved substrata of varying dimensions (4-24 microns repeat, 0.2-1.9 microns depth). Alignment to within 10 degrees of groove direction was used as our criterion for guidance. It was found that repeat spacing had a small effect (alignment is inversely proportional to spacing) but that groove depth proved to be much more important in determining cell alignment, which increased with depth. Measurements of cell alignment and examination by scanning electron microscopy showed that BHK cells and MDCK cells interacted differently with grooved substrata, and also that the response of MDCK cells depended on whether or not the cells were isolated or part of an epithelial cell island. Guidance by a multiple topographical cue is greater than could be predicted from cells' reactions to a single cue (Clark et al. Development 99: 439-448, 1987). Substratum topography is considered to be an important cue in many developmental processes. Cellular properties such as cytoskeletal organisation, cell adhesion and the interaction with other cells are discussed as being factors determining a cells susceptibility to topography.

Animals↗
PubMed1988

MHC control of cell position in vitro.

Two-dimensional sorting-out behaviour (segregation) in mixtures of pulmonary endothelial cell lines derived from congenic strains of mice was examined using dense confluent cultures in which mitosis is rare. Cell MHC type was detected by autoradiographic labelling or by immunofluorescence techniques. For autoradiography cultures of one type were previously labelled with [3H]thymidine and one component of the mixed cell types was prepared from these cultures. Autoradiographs were prepared from the fixed cultures. Counts of contiguous neighbours (labelled or unlabelled around a randomly chosen central labelled cell) were made: these were analysed statistically using a new model for such a system. The results show that segregation of a clustering type took place if the alleles of the D locus in the H-2 complex were mismatched in the mixed strains, but that matching at the IC locus (or some locus to the right of IJ) overrides the effect of D mismatch. After 2 days culture sorting-out was easily detectable when the cells were stained for their histocompatibility antigens and groups of up to 12 cells of the same type were associated together.

Animals↗
PubMed1987

Topographical control of cell behaviour. I. Simple step cues.

The photolithographic techniques of the microelectronics industry have allowed us to fabricate patterned plastic substrata to investigate contact guidance of animal tissue cells. The reactions of cells to single steps on a substratum were examined using time-lapse videorecording and scanning electron microscopy. BHK cells and chick embryonic neural cell processes exhibited gradual inhibition of crossing steps with a concomitant increase in alignment at steps dependent on increasing step height. Comparison of these cells' reactions, with those of chick heart fibroblasts and rabbit neutrophils, at a 5 micron step revealed that the influence of topography is also dependent on cell type, the neutrophils being relatively unaffected. The presence of an adhesive difference at a series of steps altered BHK cells' reactions such that the frequency of crossing was dependent on the direction of approach to a step. Although our data are consistent with Dunn & Heath's proposal (1976) that the inflexibility of the cytoskeleton of a moving cell's protrusion is the cellular property determining such reactions to topography, we have found that, on encountering a topographical feature, the response of a cell may be predictable on a probabilistic basis, i.e. the topographical feature reduces the probability of a cell making a successful protrusion and contact in a given direction, that even the largest features tested did not act as absolute barriers to cell locomotion since a small proportion of a population of cells were able to overcome them, and that other guidance cues could significantly alter a cell's response. Even in situations where it is not the primary cue in directing cell locomotion, topographical control may be an important factor during morphogenesis since it must, at the very least, influence the efficiency of other cues.

Animals↗
PubMed1987

Novel methods for the guidance and monitoring of single cells and simple networks in culture.

The effects of the topography, adhesiveness and chemistry of surfaces in modulating the behaviour of cells in vivo and in vitro have been extensively researched. However, few natural systems are simple enough to allow straightforward conclusions to be drawn, as many different cues are likely to be present at one time. Microelectronic fabrication, normally employed in making integrated circuits, can produce substrates patterned on scales highly relevant to studies of cell behaviour. In this paper, we describe progress in fabricating simple artificial substrata both at the micrometre and sub-micrometre scales. The former can be considered as models for contact guidance along other cells or axonal processes: the latter, models for guidance along aligned collagen matrices. We have systematically studied the reactions of different cell types to simple cues (steps and grooves). Additionally, it may be possible to produce fine-resolution patterns with differential adhesiveness, or with other cell-specific surface-chemical properties, such as the differential deposition of proteins, e.g. cell adhesion molecules. We also describe early results in using topographic and other cues to guide cells onto patterned metal electrodes, forming simple electrically active networks of controlled design, from which long-term recordings can conveniently be made.

Animals↗
PubMed1986

Conditions for fibroblast adhesion without fibronectin.

Conditions that permit the adhesion of BHK fibroblasts to a variety of surfaces after inhibition of protein synthesis and competition of any adsorbed fibronectin or vitronectin with the fibronectin cell-binding tetrapeptide, Arg-Gly-Asp-Ser (RGDS), are defined. Exposure of the cells to serum components at any stage in the preparation prevents cell attachment if cycloheximide or fibronectin tetrapeptide is present. If leupeptin is used cell adhesion and spreading occur even when all fibronectin synthesis is suppressed by cycloheximide inhibition, or fibronectin binding by tetrapeptide competition. The adhesions formed under these conditions appear by interference-reflection microscopy and by general properties to be identical to those formed by cells under normal culture conditions. The cell suspensions produced in the presence of leupeptin rather than other trypsin inhibitors show good adhesion at low temperatures, though the cells hardly spread at all. The results suggest that the role of fibronectin in cell adhesion should be reinterpreted in terms of its possible action as an activator rather than as a bonding molecule.

Animals↗
PubMed1984

The superoxide anion in lymphocyte transformation.

This work suggests that reactive oxygen intermediates can stimulate lymphocytes mitogenically. Incubation of human peripheral blood lymphocytes in solutions of potassium superoxide induced high levels of uptake of tritiated thymidine as did activation of monocyte production of superoxide ions using zymosan-A. Superoxide dismutase successfully reduced this stimulation but catalase and mannitol, scavengers of hydrogen peroxide and hydroxyl radicals, respectively, had no effect. The same cells are also shown to become more adhesive after superoxide treatment and we would suggest that these two phenomena may be linked.

Cell Adhesion↗
PubMed1984

The competitive effects of serum proteins on cell adhesion.

Binding curves for the adsorption of plasma fibronectin, alpha-1-antitrypsin, alpha-2-macroglobulin, ceruloplasmin, transferrin and bovine serum albumin to plain and to hydroxylated polystyrene surfaces were measured. These curves were correlated with the adhesion of BHK cells and leucocytes to these adsorbed protein surfaces in protein-free culture media. Hydroxylated polystyrene adsorbed less of alpha-1-antitrypsin, alpha-2-macroglobulin and albumin than the plain polystyrene. On the other hand the hydroxylated surfaces bound more fibronectin than the plain polystyrene surfaces. Hydroxylated polystyrene surfaces were also more adhesive for both BHK cells and leucocytes than plain polystyrene: a result confirming earlier work. The competition of fibronectin for adsorption to plain polystyrene with alpha-1-antitrypsin, alpha-2-macroglobulin and ceruloplasmin was measured and correlated with effects on cell adhesion. The results suggest that the low adhesiveness of BHK cells and leucocytes on plain polystyrene in sera-containing media is due both to the low binding of fibronectin and to the binding of serum albumin, alpha-1-antitrypsin and alpha-2-macroglobulin. The relative unimportance of fibronectin in adhesion to these surfaces is shown by the finding that cell attachment will not occur to polystyrene surfaces that have bound high levels of the antiadhesive proteins in the presence of fibronectin, even though attachment will occur in the absence of fibronectin provided that the antiadhesive proteins are lacking.

Adsorption↗
PubMed1983

Adhesion of cells to polystyrene surfaces.

The surface treatment of polystyrene, which is required to make polystyrene suitable for cell adhesion and spreading, was investigated. Examination of surfaces treated with sulfuric acid or various oxidizing agents using (a) x-ray photoelectron and attenuated total reflection spectroscopy and (b) measurement of surface carboxyl-, hydroxyl-, and sulfur-containing groups by various radiochemical methods showed that sulfuric acid produces an insignificant number of sulfonic acid groups on polystyrene. This technique together with various oxidation techniques that render surfaces suitable for cell culture generated high surface densities of hydroxyl groups. The importance of surface hydroxyl groups for the adhesion of baby hamster kidney cells or leukocytes was demonstrated by the inhibition of adhesion when these groups were blocked: blocking of carboxyl groups did not inhibit adhesion and may raise the adhesion of a surface. These results applied to cell adhesion in the presence and absence of serum. The relative unimportance of fibronectin for the adhesion and spreading of baby hamster kidney cells to hydroxyl-rich surfaces was concluded when cells spread on such surfaces after protein synthesis was inhibited with cycloheximide, fibronectin was removed by trypsinization, and trypsin activity was stopped with leupeptin.

Animals↗
PubMed1982

Graft rejection in sponges. Genetic structure of accepting and rejecting populations.

Graft rejection frequencies in a population of the sponge Ectyoplasia ferox are reported in relation to the complexity of the histocompatibility system in this species. The frequency of graft acceptance is high but we show that, despite assumptions in the literature to the contrary, this does not imply that sponges accepting each other's grafts are genetically identical. This paper reports that graft-accepting pairs of sponges can have dissimilar plasmalemmal proteins. In addition, a theoretical analysis is presented of the types of histocompatibility systems that would account for the present results and those of others. We concluded that there is no evidence that sponges have highly polymorphic histocompatibility systems. The paper also reports on the histology of graft rejection and discusses some of the ecological relevance of the findings.

Alleles↗
PubMed1981

H-2D antigens released by thymocytes and cell adhesion.

The identity and complete purification of mouse Thymocyte Interaction Modulation Factor (T IMF) is described. Use of silver-stained PAGE methods shows that previous methods of purification yield preparations containing two protein or glycoprotein bands. T IMF activity from H-2k mice can be bound to 15.5.5 monoclonal antibody columns (anti H-2 Dk) but not to 11.4.1 columns (anti H-2 Kk). The activity can be recovered from 15.5.5 columns and runs on PAGE aa a single band at approximately 34,000 Daltons. This evidence together with previous evidence relating the activity to H-2D locus argues that T IMF is a soluble H-2 D antigen fragment equivalent to a papainized H-2 fragment. Additional evidence is presented on an improved method of assay of T IMF activity, on its inactivation by enzymes and serine-esterase inhibitors and of its effect on syngeneic leucocytes and macrophages. It is shown that T IMF is not appreciably toxic cells.

Animals↗
PubMed1981

The effects of soluble cell product released by live thymocytes on lymphocyte movements in vivo.

Thymocytes have been found to release a glycoprotein when cultured for 1-2 h in serum-free media. This substance has been purified and has been called thymocyte interaction modulation factor (IMF). Thymocyte IMF is assayed in vitro by its ability to reduce the mutual adhesiveness between B lymphocytes. When thymocyte IMF is injected intravenously into mice syngeneic with the source of IMF, a rapid but short-lived leucocytosis in the blood is seen with a concomitant increase in the percentage of surface immunoglobulin (sIg) positive lymphocytes in the blood and decrease in the splenic sIg-positive lymphocyte percentage. The IMF probably causes a mobilisation of cells from the red pulp of the spleen. When radiolabelled lymphocytes are pretreated with IMF and the injected into syngeneic recipients, the localisation of cells in the liver, lymph nodes and small intestine is lower than that found with untreated cells. The mechanism of action of IMF is compared to other substances which alter lymphocyte circulation.

Animals↗
PubMed1979

H-2 restriction of contact inhibition of epithelial cells.

Medawar has suggested that the major histocompatibility gene complex (MHC) might be involved in the contact inhibition of movement shown by fibroblasts and epithelia. Contact inhibition of movement is that reaction of cells which stops the movement of one cell over another and thus leads to monolayering and other features of morphology typical of cells in culture and in vivo. By confronting epithelial outgrowths we have compared contact inhibition between syngeneic cells with that between allogeneic cells. Contact inhibition was more marked between allogeneic combinations than syngeneic combinations, when the genetic mismatch lay in certain parts of the MHC complex.

Animals↗