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Biomedical subjects

R E Stephens

Publications and source records attributed to R E Stephens.

140 records · Page 8Linked to original sources
PubMed1969

A comparative study of the isolation of the cortex and the role of the calcium-insoluble protein in several species of sea urchin egg.

A comparative study was made of the isolation of the cortex in the eggs of several sea urchin species. Since the isolation method developed by Sakai depends on the presence of magnesium in the medium, the protein composition of the cortex was investigated to determine whether the protein component of the egg described by Kane and Hersh which is gelled by divalent ions, is present in these cortices. Isolation of the cortex was found to require the same divalent ions at the same concentrations as protein gelation, and in the eggs of some species much of the gel protein of the cell was found in the isolated cortical material. In the eggs of other species a smaller fraction of this protein was found in the isolated cortex, although it was more concentrated there than in the endoplasm, and in one species this protein appeared to be uniformly distributed throughout the cell. These results indicate that this protein is localized in the cortical region of the eggs of some species of sea urchin, possibly in the cortical granules, but also point up the fact that results from one species cannot be uncritically extrapolated to others.

Animals↗
PubMed1967

The mitotic apparatus. Physical chemical characterization of the 22S protein component and its subunits.

The major 22S protein of the hexylene glycol-isolated mitotic apparatus has been characterized from spindle isolates and extracts of whole eggs and acetone powders of eggs from the sea urchins Strongylocentrotus purpuratus, Strongylocentrotus droebachiensis, and Arbacia punctulata. The protein is free of nucleotide, lipid, and ATPase activity. Essentially identical in amino acid composition, proteins from these species show a relatively high content of glutamic and aspartic acids and are fairly rich in hydrophobic amino acids. Optical rotatory dispersion studies indicate a helical content of about 20%, a value consistent with the proline content of the protein. The purified proteins have sedimentation rates in the range of 22-24S, diffusion constants of 2.4-2.5F, intrinsic viscosities of 3.7-4.3 ml/g, a partial specific volume of 0.74, and an average molecular weight of 880,000. Electron microscopy indicates a globular molecule with dimensions of approximately 150 by 200 A; such size and symmetry are consistent with hydrodynamic measurements. The 22S protein yields 6-7S, 9-10S, and 13-14S subunits below pH 4 or above pH 11. The 13-14S component has an estimated molecular weight of 600,000-700,000. A 5-6S particle is formed in 8 M urea or 5 M guanidine hydrochloride, while at pH 12 the 6-7S subunit is seen; each particle has a molecular weight of 230,000-240,000. In 8 M urea plus 2% mercaptoethanol or at pH 13, the molecular weight becomes 105,000-120,000; under these conditions the particle sediments at 2.5-3S and 4S, respectively. On the basis of these molecular weights, the 6-7S, 9-10S, 13-14S, and the parent 22S particle should be dimer, tetramer, hexamer, and octamer, respectively, of the 105,000-120,000 molecular weight subunit. The various subunits will reform the 22S particle when returned to neutral buffer, with the exception of the mercaptoethanol-treated urea subunit where breakage of disulfide bonds results in a polydisperse aggregate. The 22S particle itself is not susceptible to sulfhydryl reagents, implying either that the disulfide bonds are inaccessible or that they are unnecessary for maintenance of tertiary structure once the 22S particle has formed from subunits.

Acids↗
PubMed1965

Anomalous contraction of invertebrate striated muscle.

The phenomenon of A band shortening or contraction has been investigated in glycerinated myofibrils of Pecten irradians, Homarus americanus, Cambarus virilis, and Limulus polyphemus through the techniques of ultraviolet microbeam inactivation and polarization microscopy. With the former method, it has been shown that these muscles, even though exhibiting the shortening effect, contract in a manner consistent with only the sliding filament model. Intrinsic birefringence studies have indicated no significant changes in mass distribution or orientation within the shortened A bands. Except in the case of Limulus muscle, the shortening effect was seen only in contraction under tension. The magnitude of this anomalous phenomenon was dependent upon glycerination time and has been duplicated in rabbit psoas muscle through brief trypsin treatment. A band shortening could not be observed in glutaraldehyde-fixed muscle or in myofibrils glycerinated for only short periods. It has been concluded that the phenomenon of A band contraction is an artifact induced by the glycerination procedure, possibly through weakening of the sarcomere structure. However, the fact that the A band shortens under tension rather than lengthens poses an interesting paradox.

Adenosine Triphosphate↗
PubMedDate not supplied

Connective tissue synthesis by cultured scleroderma fibroblasts. I. In vitro collagen synthesis by normal and scleroderma dermal fibroblasts.

The authors have been unable to demonstrate an increase in collagen synthesis by fibroblasts isolated from sclerodermatous skin. In order to elucidate this problem further, scleroderma fibroblasts were biopsied from upper dermis, from lower (including subcutaneous) dermis, and from adjacent clinically noninvolved skin. All cell lines failed to show a significant increase in collagen synthesis when they were compared to control fibroblast lines. One difference among them was that fibroblasts from involved areas showed a rate of collagen synthesis equal to or less than cells isolated from adjacent clinically noninvolved sites.

Adolescent↗
PubMedDate not supplied

Tartaric acid-induced cough and the superior laryngeal nerve evoked potential.

The purpose of this study was to stimulate the laryngeal cough reflex using a nebulized, mild chemical irritant and to record an associated laryngeal evoked potential from the internal branch of the superior laryngeal nerve. The laryngeal evoked potential was obtained on ten normal subjects from the right internal branch of the superior laryngeal nerve. The electrodiagnostic setup included an active electrode placed just below the hyoid bone with a 4-cm separation and distal reference. A ground electrode was placed between the active and reference electrodes. The receptors and internal branch of the superior laryngeal nerve were stimulated by inhalation of a nebulized 20% solution of tartaric acid and normal saline. The time line was triggered by a pneumatic switch on initial inspiration of the nebulized tartaric acid. The electrodiagnostic settings were set at a sweep speed of 1 ms/division, a gain of 10 to 20 microV/division, and 20 to 2,000 filters. There were 132 variables recorded from the internal branch of the superior laryngeal nerve of the ten subjects. The mean peak distal latency was 1.66+/-0.42 ms with a 1.6 median, 1.6 mode, and 0.17 variance. The duration was 0.41 ms, and amplitude was 5.19+/-2.91 microV. In conclusion, the laryngeal evoked potential, the afferent component of the involuntary cough reflex, can be recorded from the internal branch of the superior laryngeal nerve after inhalation of tartaric acid-induced cough.

Administration, Inhalation↗
PubMedDate not supplied

Modulation of biological processes by mineral fiber adsorption of macromolecules in vitro.

Three classes of macromolecules (i.e., DNA, RNA, and protein) were shown to be adsorbed to asbestiform minerals. The cytotoxicity exerted by the fibers on a normal human fibroblast cell line, which may be an indicator of the carcinogenic potential of mineral fibers, correlated positively with the degree of macromolecular adsorption of the fiber, namely: chrysotile greater than amosite greater than glass fiber. Asbestiform fibers also induce an alteration in in vitro DNA hydrolysis by bovine pancreatic deoxyribonuclease. This phenomenon suggests that adsorption by asbestiform minerals may modulate biological processes by inducing a conformational change in biological macromolecules as a result of coulombic interaction between the surface charge of the fiber and the hydrophilic groups on the macromolecule.

Adsorption↗