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Biomedical subjects

R D Allen

Publications and source records attributed to R D Allen.

At least 19 recordsLinked to original sources
PubMed1992

Transplantation of the endocrine pancreas in 1992.

In 1992, transplantation of the endocrine pancreas is placed at the interface between laboratory research and clinical medicine. Unlike other forms of transplantation, it is not life saving, and yet its potential to treat all patients with insulin dependent diabetes is limited only by the availability of donated organs. Arguably, the long term glucose homoeostasis provided by vascularised pancreas transplantation is the standard by which other forms of endocrine pancreas transplantation (islet cell, fetal islet, and xenogeneic transplantation) must be judged. For the small number of type I diabetic Australians who develop end-stage renal failure and would otherwise require a renal transplant, the combined transplant procedure is a technically viable treatment option and, with some justification, the treatment of choice.

Diabetes Mellitus, Type 1↗
PubMed1979

Transformation and motility of human platelets: details of the shape change and release reaction observed by optical and electron microscopy.

Blood platelets from 10 normal human subjects have been examined with a sensitive differential interference contrast (DIC) microscope. The entire transformation process during adhesion to glass is clearly visible and has been recorded cinematographically, including the disk to sphere change of shape, the formation of sessile protuberances, the extension and retraction of pseudopodia, and the spreading, ruffling, and occasional regression of the hyalomere. The exocytosis of intact dense bodies can be observed either by DIC microscopy, or by epifluorescence microscopy in platelets stained with mepacrine. Details of fluorescent flashes indicate that the dense bodies usually release their contents extracellularly, may do so intracytoplasmically under the influence of strong, short wavelength light on some preparations of mepacrine-stained platelets. The release of one or more dense bodies leaves a crater of variable size on the upper surface of the granulomere. Such craters represent the surface component of the open canalicular system and their formation and disappearance can be directly observed. Because these techniques permit quantitation of several parameters of motility which are not readily observable by other techniques, it is suggested that high extinction DIC microscope examination may become a rapid and useful method of studying congenital and acquired platelet disorders. Many features of platelet transformation have been confirmed and extended by scanning electron micrographs. These can in turn be interpreted by reference to time-lapse films of living platelets.

Blood Platelets↗
PubMed1979

Axenic Paramecium caudatum. I. Mass culture and structure.

To establish and grow Paramecium caudatum in mass axenic culture the culture medium of Soldo, Godoy & van Wagtendonk was modified by substituting phosphatidylethanolamine (PE) for TEM-4T and by a 10-fold increase in folic acid. Population densities of 4000 to 6000 cells/ml and a generation time of 20-26 h are regularly obtained. Optimal growth is obtained with PE-stigmasterol ratios between 40:1 to 400:1. Cells from 1-day-old axenic cultures have many lipid bodies aggregated in clumps (which disappear in 2 to 3 days) as well as foci of rough endoplasmic reticulum bordered by dictyosomes. The latter suggests a very active metabolism. Crystalline sheets found in both food vacuoles and lysosomes presumably play a role in digestion. Axenically grown cells also have abundant Golgi bodies (dictyosomes) and by late log phase become filled with lysosomes.

Animals↗
PubMed1979

Structure, protein composition and birefringence of the costa: a motile flagellar root fibre in the flagellate Trichomonas.

The costa is a rod-shaped intracellular organelle lying in the cytoplasm immediately below the undulating membrane. In certain large species of Trichomonas (T. gigantea, T. termopsidis and an undescribed species from the termite Porotermes adamsoni) this organelle is motile. Bending waves are transmitted along the length of the costa, in either direction. It is shown that the bending is actively produced by the costa itself. The form of the movements is described in detail. The costa is birefringent. At the point at which bending occurs there is a sharply localized reduction in birefringence. Electron microscopy shows that the costa is composed of longitudinally running lamellae, 2--3 nm thick and spaced 12 nm apart. These are connected to transversely running elements spaced at intervals of about 37 nm. The lamellae occur in two alternative configurations: straight and zig-zag. Bending probably results from a local, transient change from the straight to the zig-zag configuration. This would account for the local change in birefringence which accompanies bending. Polyacrylamide gel electrophoresis of isolated costas shows them to contain a number of protein components, of which the principal one has a molecular weight of about 90,000. Preliminary cytochemical evidence is presented for ATPase activity in the costa. The costa is a type of motile system distinct from any hitherto described.

Adenosine Triphosphatases↗
PubMed1979

Membrane recycling at the cytoproct of Tetrahymena.

Exocytosis and membrane recycling at the cytoproct (cell anus) of Tetrahymena pyriformis were studied using thin-section electron microscopy. Single cells were fixed at specific times relative to the elimination of the vacuole's contents--before elimination, at elimination, 3--5 s and 10--15 s following elimination. The closed cytoproct is distinguished from other pellicular regions by a single membrane at the cell surface which is circumscribed by an electron-opaque flange that links or welds the plasma membrane to the underlying alveolar margins. Microtubules originating in the flange pass inward where they lie over, and possibly guide, the approaching food vacuoles to the cytoproct. Food facuoles near the cytoproct are also accompanied by coats of microfilaments. These microfilaments appear to be active in the channelling and endocytosis of food vacuole membrane. Upon cytoproct opening the plasma membrane and food vacuole membrane fuse. Elimination seems to be essentially passive and is accomplished by re-engulfment of the old food vacuole membrane which is constantly associated with microfilaments. Reengulfment of all the food vacuole membrane requires 10--15 s and results in a closed cytoproct. The membrane remnants embedded in microfilaments form a cluster under the closed cytoproct. At the periphery of this cluster remnants take the shape of 70--130-nm spherical vesicles or 0.2-micrometer-long flattened vesicles.

Animals↗
PubMed1979

Hand-mirror cell leukemia associated with mental retardation: immunologic, chromosome, and morphological studies.

Cycochemical, morphological, immunologic, and cytogenetic studies were carried out on hand-mirror cells (HMC) from a mentally retarded patient with a constitutional chromosome abnormality, 46,XX,r(21), and acute lymphoblastic leukemia. Scanning electron and differential interference contrast microscopy showed microspikes on the uropodia, but little evidence of cellular motility, despite formation and disappearance of individual uropodia in cell suspensions. The cells rosetted with sheep erythrocytes, suggesting T-cell origin. Cells derived from the bone marrow (80% HMC) showed a high degree of polyploidy (60%) and a bimodal chromosome number of 49 (49,XX,+10,-21, +3 rings) and 94 (6 no. 10, 3 no. 18, 2 no. 21 chromosomes, 3 ring chromosomes, plus 4 copies of each other chromosome).

Bone Marrow↗
PubMed1977

Electrocardiographic exercise test in patients with abnormal T waves at rest.

The results of submaximal ECG exercise test were evaluated in six leads recorded simultaneously in two groups of patients with T-wave abnormalities in one or more of Leads I, II, and V4-6. Group I included 185 patients with documented ischemic heart disease (IHD) and Group II 28 patients in whom IHD appeared unlikely. The test was positive in 88 per cent of patients in Group I and in 4 per cent of patients in Group II. In the majority of patients in both groups the T wave either did not change or became more positive or less negative after exercise. The pattern of exercise-induced T-wave changes was similar in patients with and without IHD, and was influenced predominantly by the physiologic effects of exercise. T-wave normalization after exercise occurred frequently in patients with and without IHD, and in patients with positive and negative exercise tests. Our results suggest that T-wave abnormalities, not caused by hypertrophy, conduction disturbances, drugs, or electrolyte imbalance, do not modify the results of submaximal ECG stress test, and that behavior of T wave after exercise does not alter the interpretation of the postexercise ECG. The independent behavior of the S-T segment and T wave after exercise in consistent with the theory that the S-T segment and the T wave are generated by different components of the ventricular action potential.

Adult↗
PubMed1977

Phase-randomized laser illumination for microscopy.

A simple apparatus is described that phase randomizes the output of a continuous argon ion laser, so that it may be used as a source of high intensity, monochromatic light for microscopy. The phase-randomizing device can be used with any laser, polarized or unpolarized, and of any desired power output and wavelength, including dye lasers for spectral studies. The randomizing system can be adapted to any light microscope and any optical system including bright-field, phase-contrast, Nomarski differential-interference, dark-field, and split-beam interference systems such as the Jamin-Lebedeff System. It can be used for a variety of photometric and photographic studies. The 514-nm wavelength appears to be relatively harmless to a variety of cells.

Lasers↗
PubMed1977

Behaviour of kinetochore fibres in Haemanthus katherinae during anaphase movements of chromosomes.

A laser light source along with a new method of preparing endosperm cells of Haemanthus katherinae for differential interference contrast (DIC) microscopy has led to increased visibility of kinetochore fibres. Little information is available concerning the behaviour of these fibres during anaphase in living cells. In metaphase, kinetochore fibres are seen as distinct bundles of microtubules, here referred to as 'filaments', extending from the kinetochore to the 'diffuse' pole. They possess an apparent globular substructure which corresponds to the moving 'particles or states' described previously from ciné films. In early anaphase, the filaments of each kinetochore fibre lose their parallel orientation characteristic of metaphase and splay out so that the more peripheral filaments intermingle with those of other kinetochore fibres. This process begins at the poles and proceeds as a wave toward the kinetochores as chromosomal movement progresses. This behaviour has been examined in relation to a number of proposed models for the mechanism of chromosome movement and has been found to place some constraints on some models but to be consistent with any model that hypothesizes that chromosomes move as a consequence of cumulative cohesive lateral interactions of microtubules.

Anaphase↗
PubMed1976

Membrane behavior of exocytic vesicles. II. Fate of the trichocyst membranes in Paramecium after induced trichocyst discharge.

A specific exocytic process, the discharge of spindle trichocyts of Paramecium caudatum, was examined by means of the electron microscope. This exocytosis is induced by an electric shock simultaneously in nearly all of the trichocysts (ca. 6,000-8,000) of a single cell. Single paramecia were subjected to the shock and then fixed at defined times after the shock so that the temporal sequence of the pattern of changes of the trichocyst membranes after exocytosis could be studied. The trichocyst vacuoles fuse with the plasma membrane only for the length of time required for expulsion to take place. After exocytosis, the membrane of the vacuole does not become incorporated into the plasma membrane; rather, the collapsed vacuole is pinched off and breaks up within the cytoplasm. The membrane vesiculates into small units which can no longer be distinguished from vesicles of the same dimensions that exist normally within the cell's cytoplasm. The entire process is completed within 5-10 min. These results differ from the incorporation of mucocyst membranes into the plasma membrane as proposed for Tetrahymena.

Animals↗