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Biomedical subjects

W R Colquhoun

Publications and source records attributed to W R Colquhoun.

6 recordsLinked to original sources
PubMed1985

Sputter shadowing improved by using a tungsten target.

This work builds upon a previous paper (W. Colquhoun, 1984, J. Ultrastruct. Res. 87, 97) in which a sputter shadowing device was briefly described. The device allowed TEM specimens to be shadowed in a conventional sputter coater. Images obtained by sputter shadowing with a standard Au/Pd target were of good quality but were slightly inferior to the best that could be obtained by e--beam evaporation of tungsten. Here we show that construction and use of a tungsten target greatly improves the quality of the sputter shadowed deposit. Images of DNA and ribosomal subunits contrasted by sputter shadowing with tungsten are shown. The DNA images indicate that sputter shadowing with tungsten is a gentle contrasting technique. The sputter shadowed images of the 30 S ribosomal subunits show the major features of the particle revealed by evaporation shadowing using the most sophisticated of methods in that technology. Advantages of sputter shadowing are discussed and a rationale for the improved grain obtained by sputtering tungsten is suggested.

Bacteriophage lambda↗
PubMed1985

A method for removing stain precipitate and destaining sections.

Subjecting electron microscope sections to NaOH treatment removes stain precipitate from the section surface. The alkali treatment also extracts stain from the tissue itself. Following this treatment, sections can be restained to obtain clean images. Alternatively, after being viewed or photographed using one stain and then destained, the same sections can be treated with a different stain to obtain additional histochemical information.

Animals↗
PubMed1984

Sputter shadowing.

A device has been constructed which allows specimens to be shadowed in a conventional sputter water. This process of sputter shadowing lends to specimens a contrast suitable for imaging in the transmission electron microscope (TEM). The process has the practical advantages over metal evaporation shadowing of lower instrumentation costs, less user training, and less time expenditure per shadowing operation. It provides on a single grid a spectrum of shadowing contrasts from which optimal imaging for a particular specimen can be chosen. The process minimizes radiant and metal deposition heating of the specimen and, thereby, may better preserve its structure during the contrasting procedure. The grain resulting from sputter shadowing differs significantly from that obtained by metal evaporation shadowing and the possibility for using this difference to improve resolution in shadowed preparations is discussed.

Microscopy, Electron↗
PubMed1983

Lymphoblastoid cell variant in contact-mediated cell spreading.

We have isolated a clone of human lymphoblastoid cells that is capable of undergoing the phenomenon of contact-mediated cell spreading in vitro. We have detected this behavior when using both transmission electron microscopy (TEM), and differential interference contrast microscopy. Upon cell-cell contact, cells become loosely adherent and then begin to extend cellular processes that contact other cells and the substrate. We have also selected a variant clone that has lost the capability for cell spreading. The adhesions-defective variant becomes adhesion-positive and appears morphologically identical with the adhesive cells only in response to specific amino sugars. In the presence of those sugars the adhesion response is correlated with a shift in the apparent molecular weight of an iodinatable component. We propose that contact-mediated cell spreading in lymphoblastoid cells is mediated by a non-transferable cell surface-associated glycoconjugate. The synthesis of that glycoconjugate is defective in the non-adhesive clone, unless the cells are grown in glucosamine or mannosamine.

Cell Adhesion↗
PubMed1980

Structure of the chromosomal material in inactive nuclei of chicken red blood cells.

Electron microscope sections have been cut of chicken red blood cell nuclei by a novel procedure that produces zones of material below 100 A in thickness. After fixing and staining, electron dense structures are observed that have dimensions closely correlating with those determined for nucleosomes. These structures appear as wedge-shaped or as circular objects with a diameter of approximately 90-100 A. Five to eight of these objects are arranged in a spiral around a central core giving rise to a 250-300 A structure which may represent a superbead or a cross section of a solenoidal fibre.

Animals↗