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Biomedical subjects

R D Allen

Publications and source records attributed to R D Allen.

28 records · Page 2Linked to original sources
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↗
PubMed1976

Painless ST-segment depression in patients with angina pectoris. Correlation with daily activities and cigarette smoking.

Ambulatory electrocardiographic monitoring was employed in 33 patients with angina pectoris and abnormal stress tests to determine the frequency with which myocardial ischemia manifested by painless ST-segment depression occurred during normal activity. ST-segment depression occurred in 24 patients during the monitoring period; and in 21, it occurred either solely in the absence of pain or both with and without pain. Of 109 recorded episodes of ST-segment depression, 61 percent were painless. The frequency of painless ST-segment depression was independent of activity other than automobile driving, during which all episodes were painless. In patients who smoked cigarettes, ST-segment depression was more common while smoking, but the incidence of painless ST-segment depression was not altered. The study indicates that ST-segment depression occurs more commonly in the absence than in the presence of chest pain and that ambulatory electrocardiographic monitoring is a useful method of determining the frequency of myocardial ischemia during normal daily activity.

Adult↗
PubMed1975

Evidence for firm linkages between microtubules and membrane-bounded vesicles.

Direct evidence is presented in support of the widely held idea that membrane-bounded vesicles can bind firmly to microtubules. This is shown in P. caudatum which contains ribbons of straight microtubules located in open cytoplasm and uniquely associated with the disk-shaped vesicles. These vesicles frequently lie flat against the face of the ribbons at a constant distance of 30-40 nm. Under certain conditions the ribbons are compressed into zigzag pattern, but the vesicles continue to maintain their 30-40 nm spacing with the tubules and The author's interpretation of this phenomena is that the vesicles and the microtubules are strongly bound together. This interaction appears to be via a filamentous material rather than bridges.

Animals↗
PubMed1975

Cytochemical localization of peroxisomes in Tetrahymena pyriformis.

Pronounced staining of Tetrahymena pyriformis peroxisomes was demonstrated when glutaraldehyde-fixed cells were incubated in an alkaline medium containing 3,3'-diaminobenzidine and hydrogen peroxide. A variable amount of electron-opague deposit was observed when cells were incubated in diaminobenzidine and H2O2 for 1 hr while an intense deposit followed incubation for 4 hr in the same medium. The staining was abolished completely when 3-amino-1,2,4-triazole, KCN or NaN3 was added to the incubation medium. Based on these cytochemical observations and the morphologic identification by size, shape and other ultrastructural details, it is suggested that this study presents evidence for a conclusive morphologic identification of Tetrahymena peroxisomes.

Amitrole↗