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Biomedical subjects

A Nicol

Publications and source records attributed to A Nicol.

At least 19 recordsLinked to original sources
PubMed1992

Cell adhesion and growth on synthetic elastomeric matrices containing Arg-Gly-Asp-Ser-3.

Synthetic elastomeric polypeptide matrices based on the repeating amino acid sequences of elastin have biophysical and biological properties which are favorable for prosthetic materials. An important requirement envisaged for some applications is the ability to support cell adhesion and growth. The X20-poly-(GVGVP), the gamma-irradiation cross-linked elastomeric matrix based on the repeating pentamer Val-Pro-Gly-Val-Gly, and X20-poly[n(GVGVP), (GRGDSP)] containing the covalently incorporated cell adhesion sequence Arg-Gly-Asp-Ser (RGDS) were synthesized. These matrices were tested for their ability to support the adhesion and growth of bovine aortic endothelial cells and of bovine ligamentum nuchae fibroblasts. Adhesion experiments carried out in albumin-containing media showed that matrices containing 60:1, 40:1, and 20:1 ratios of (GVGVP):(GRGDSP) supported maximal cell attachment, that matrices containing 100:1 exhibited an intermediate level of attachment and that matrices composed of 500:1 and (GVGVP) alone were very poor supports for cell attachment. Serum in the media promoted submaximal cell attachment to X20-poly(GVGVP) but did not permit substantial cell growth. Cell growth was supported by matrices having high ratios of (GRGDSP). Ratios of 60:1, 40:1, and 20:1 supported three population doublings of endothelial cells over 3 days resulting in confluent matrix-adherent monolayers. Ratios of 40:1 and 20:1 similarly supported the growth of fibroblasts.

Amino Acid Sequence↗
PubMed1987

Labeling of structural elements at the ventral plasma membrane of fibroblasts with the immunogold technique.

We investigated the organization of two structural elements (microfilaments and clathrin coated structures) at the ventral plasma membrane in fibroblasts. The methods employed included exposure of the inner face of the ventral plasma membrane by lysis-squirting, labeling the exposed structures with specific antibodies conjugated with colloidal gold, and platinum-carbon replica techniques. The results demonstrate that this regimen combines good ultrastructural preservation with unambiguous identification of structural elements associated with the plasma membrane. This method is therefore reliable and can be generally used to explore in detail the ultrastructural organization of the plasma membrane.

Actin Cytoskeleton↗
PubMed1987

A new type of substratum adhesion structure in NRK cells revealed by correlated interference reflection and electron microscopy.

The substratum adherent membrane of NRK cells in vitro has been studied using correlated interference reflection and surface replica electron microscopy. Structures visualized by interference reflection microscopy were identified in the subsequently prepared platinum-carbon replicas of the adherent membranes. Substratum adherent membranes were prepared using a hypotonic shock/cell shearing technique (lysis-squirting). Typically 20% of the original ventral membrane surface area and 50% of the original focal adhesion number were retained. Microfilament bundle termini, clathrin-coated sheets and pits, cytotic vesicles having a ridged surface and groups of membrane associated particles were well preserved in the replicas. Two types of isolated adhesion structures were found after lysis-squirting. In addition to typical elongate focal adhesions containing actin and vinculin, we report the existence of adherent membrane patches lacking microfilament bundles and negative for vinculin labelling, but coated with clathrin and identifiable in interference reflection microscopy as less dark than focal adhesions and having dot, U- or sinusoidal shapes.

Actin Cytoskeleton↗
PubMed1983

Bends made easy.

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Fracture Fixation, Internal↗
PubMed1982

Fibronectin, intercellular junctions and the sorting-out of chick embryonic tissue cells in monolayer.

A hierarchy of relative cohesiveness in monolayer of four different embryonic chick tissues was determined in a previous study. The hierarchy is: corneal epithelium congruent to liver parenchyma greater than pigmented epithelium greater than limb bud mesenchyme. The purpose of this paper is to describe the correlation between these adhesive relationships and, firstly, the amount of the adhesive glycoprotein, fibronectin, associated with the cells and, secondly, the morphology of their intercellular contacts. Fluorescent antibody staining of the cells with anti-fibronectin antibody showed that limb bud mesenchyme cells, the most weakly cohesive, had much more fibronectin than the other cell types. Thus there was a negative correlation between the amount of fibronectin and cellular cohesiveness. Analysis of intercellular contacts by electron microscopy showed that the most strongly cohesive cell types, corneal epithelium and liver parenchyma, were also those that possessed desmosomes.

Animals↗
PubMed1982

Effects of vitamin A on the behaviour of migratory neural crest cells in vitro.

It has been proposed elsewhere that the teratogenic effects of retinoids on craniofacial morphogenesis are caused by a disturbance of the migration of cranial neural crest cells. The effects of 3.5 X 10(-5) M and 3.5 X 10(-6) M-retinol on the migration of avian neural crest cells in vitro have been investigated by monitoring cell morphology, locomotory behaviour, fibronectin distribution and actin-microfilament organization. Retinol retards migration by affecting cell-to-substratum adhesiveness. Cells exposed to medium containing retinol are less adherent to the substratum, and although the cell surface is very mobile, are unable to extend or maintain lamellipodia. As a consequence the cells do not actively translocate. Fibronectin distribution at the cell surface is sparse, possibly as a result of shedding, and actin distribution remains diffuse. At the retinol molarities used all these effects are reversible. Thus cells allowed to recover in normal medium flatten out, display lamellipodia and commence active translocation. Fibronectin becomes organized into a fibrillar array and actin microfilaments become organized into cables. The period needed for this recovery is directly related to the molarity of retinol during the initial exposure; after recovery the retinol-treated cells are virtually indistinguishable from control cells. We propose that in vivo the effects of retinoids might be to impair cell-extracellular matrix interaction, thus impeding a cell's ability to migrate through that matrix. Contrary to previous suggestions, the in vivo effects are probably not in any way 'specific' to neural crest cells but are more accurately considered as 'selective', in that any cell undergoing migration would be similarly affected.

Actins↗
PubMed1979

The sorting out of embryonic cells in monolayer, the differential adhesion hypothesis and the non-specificity of cell adhesion.

It has been reported previously that sorting out of chick embryonic liver parenchyma and limb bud mesenchymal cells would take place in monolayer culture. The distribution of cell types obtained (liver formed the internal, discontinuous phase) was interpreted in terms of the differential adhesion hypothesis. It was suggested that, in monolayer, liver cells were more cohesive than limb bud cells. In this paper we set out to extend the previous observations with 2 particular questions in mind: (i) Is sorting out in monolayer a general phenomenon occurring between a wider range of cell types? (ii) Can evidence be provided for or against the interpretation of results in terms of the differential adhesion hypothesis? Sorting-out experiments were conducted on circular hydrophilic islands, on an otherwise hydrophobic substratum. Under these conditions, sorting-out in monolayer was obtained with binary combinations of 4 chick embryonic tissue types: liver parenchyma, limb bud mesenchyme, pigmented epithelium of the eye and corneal epithelium. With every combination but one, the cells of one type surrounded the cells of the other type, generating what we have called a 'circle-within-a-circle' configuration. With the remaining combination, liver parenchyma and corneal epithelium, only localized sorting was obtained. The 'circle-within-a-circle' configuration is consistent with an interpretation in terms of the differential adhesion hypothesis, according to which the distribution of cells is determined by the relative strengths of cohesions between their lateral surfaces. In direct support of this is the finding from plating the different cell types at sub-confluent density on hydrophilic substrata that limb bud is the cell tye having the weakest lateral cohesion in monolayer. Limb bud surrounded the other 3 tissues on hydrophilic island. A hierachy of lateral cohesiveness between the 4 cell types has been constructed. It is unlikely that the results can be explained in terms of specific cohesion. When plated together at subconfluent density, the 3 epithelial cell types aggregate together to form mixed monolayered islands, suggesting that they share common adhesive mechanisms.

Animals↗
PubMed1978

An assessment of the accuracy of modern endoscopic diagnosis of oesophageal stricture.

The results of 135 fibreoptic endoscopic examinations of oesophageal strictures carried out in a district general hospital are reported. The endoscopic diagnosis was correct in 90 per cent, uncertain in 3 per cent and incorrect in 7 per cent of these cases. This study indicates that endoscopic examination should include tissue sampling; this not only allows a precise tissue diagnosis to be made but also is shown to increase the accuracy of diagnosis. Tissue sampling should include cytological as well as histological material. Analysis of cases of stricture correctly diagnosed has shown that target biopsy and brush cytology each makes a significant contribution to diagnosis. The routine collection of cytological specimens in addition to the more commonly obtained histological specimens in addition to the more commonly obtained histological speciments is strongly advocated. The natural history of malignant oesophageal strictures in this study is reviewd. The mean survival in 58 cases was 6.9 months.

Adult↗
PubMed1978

Mutual cohesion and cell sorting-out among four species of cellular slime moulds.

Interspecific cell cohesion among 4 species of cellular slime moulds, Dictyostelium discoideum, D. mucoroides, D. purpureum and Polysphondylium violaceum has been studied. Binary mixtures of aggregation-stage cells of the 4 species were shaken in suspension, one species of each pair being labelled with [3H]thymidine. Cell aggregates were sampled at intervals over 24 h and their composition examined by autoradiography. The following results were obtained: (i) Cells of each species were capable of cohesion with those of the other 3 species. (ii) In general cells of both species in any mixture were present in aggregates after 1 h, but were not localized according to species. (iii) Within 8-h aggregates cells of different species were regionally localized, i.e. sorting-out appeared to have taken place. (iv) 24-h aggregates were more varied: in mixtures of Dictyostelium species, the different species were localized within the aggregates; in mixtures of Dictyostelium species with Polsphondylium, there was a tendency for cells of the different species to become segregated into completely separate aggregates. The significance of these results in relation to both previous descriptive work and recent biochemical studies on the mechanism of slime mould cell cohesion is discussed.

Adhesiveness↗