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Biomedical subjects

R Walter

Publications and source records attributed to R Walter.

At least 127 records · Page 7Linked to original sources
PubMed1984

Distribution of hematoporphyrin derivative in the rat 9l gliosarcoma brain tumor analyzed by digital video fluorescence microscopy.

A digital video fluorescence microscopy technique was used to evaluate the distribution of hematoporphyrin derivative (HPD) in the rat intracerebral 9L gliosarcoma brain-tumor model at 4, 24, 48, and 72 hours after intravenous administration of 10 mg/kg of the drug. Compared to surrounding normal brain, there was significant preferential uptake of HPD into the tumor. In sections surveyed, fluorescence reached a maximum value by 24 hours; however, only 33% to 44% of the tumor was fluorescent. In contrast, fluorescence within the surrounding normal brain was maximum at 4 hours, but was present in less than 1% of the brain tissue evaluated. The effect of HPD sensitization to a laser light dose (633 nm) of 30 joules/sq cm delivered through the intact skull was evaluated histologically in 10 rats. A patchy coagulation necrosis, possibly corresponding to the distribution of HPD fluorescence seen within the tumor, was observed. There was evidence that photoradiation therapy (PRT) affects defective tumor vasculature and that a direct tumor cell toxicity spared normal brain tissue. Despite these findings, limited uptake of HPD in tumor and the brain adjacent to tumor may decrease the effectiveness of PRT in the 9L gliosarcoma brain-tumor model. Because of the similarity between the capillary system of the 9L tumor and human brain tumors, PRT may have a limited therapeutic effect in patients with malignant brain tumors.

Animals↗
PubMed1982

Laser-stimulated fluorescence of submicrometer regions within single mitochondria of rhodamine-treated myocardial cells in culture.

A focused laser beam of 442 nm was used to stimulate fluorescence in 0.5-micrometer spots in single mitochondria of myocardial and endothelial cells in culture. Cells were treated with rhodamine 6G or 123 in order to render the mitochondria fluorescent. Rhodamine 123-treated cells exhibited a gradual decrease in fluorescence over several minutes, whereas the rhodamine 6G-treated myocardial cells exhibited three distinct patterns of variable fluorescence intensity. These patterns were detected at different points within the same mitochondrion or in different mitochondria. Mitochondria from nonmyocardial endothelial cells did not exhibit any variable intensity patterns of fluorescence. Electron microscopy revealed no ultrastructural damage attributable to laser exposure of the mitochondria. The variable fluorescence patterns are hypothesized to be indicative of localized alterations in molecules or ions at the suborganelle level.

Animals↗
PubMed1982

In vitro cellular effects of hematoporphyrin derivative.

Several in vitro cell systems were exposed to hematoporphyrin derivative (HPD): established lines of rat kangaroo epithelial kidney; normal mouse embryonic fibroblasts; and differentiated neonatal rat myocardial cells. The uptake of HPD (25 to 100 micrograms/ml) by individual cells occurred rapidly over a 2-hr period and leveled off by 24 hr. HPD was excreted from cells by 48 hr after exposure. However, a low level of HPD (above background) was maintained in cells for up to 4 days following cessation of exposure. Intracellular binding of HPD was to mitochondria as demonstrated by fluorescence microscopy. HPD was also shown to have a growth-inhibiting effect on rat kangaroo cells without added light. The growth effects on mouse cells were less marked.

Animals↗
PubMed1982

Long-term study of virus contamination of surface water in the German Democratic Republic.

Between 1 January 1970 and 31 December 1979, a study of the concentration of viruses in surface water was carried out by 4 virological laboratories in different regions of the German Democratic Republic. All these laboratories used the same methods for virus detection.Altogether 1908 samples from 30 sampling points were evaluated. The rate of virus isolation ranged from 8% to 92% with a mean of 20%. There were considerable differences in isolation rate among the sampling points, and the rate for any particular point varied from year to year.The mean value of virus concentration, determined by the most probable number technique, was 2.7 cytopathogenic units (CU) per litre, while the maximum was 22.1 CU/litre. Viruses seen throughout the 10-year investigation included poliovirus, types 1, 2, and 3, echovirus types 6, 11, and 30, and coxsackievirus B 3 and B 5; echovirus 7 and 24, coxsackievirus B 1, and adenovirus 5 were seen occasionally. The results of the study reflected the high level of use of surface waters in the German Democratic Republic.Where water is intended for human use, e.g., as drinking-water or for recreation, reasonable safety measures, such as water treatment and disinfection, should be taken, in order to ensure that the level of viral contamination is within the permissible limits.

Germany, West↗
PubMed1981

Laser microsurgery in cell and developmental biology.

New applications of laser microbeam irradiation to cell and developmental biology include a new instrument with a tunable wavelength (217- to 800-nanometer) laser microbeam and a wide range of energies and exposure durations (down to 25 X 10(-12) second). Laser microbeams can be used for microirradiation of selected nucleolar genetic regions and for laser microdissection of mitotic and cytoplasmic organelles. They are also used to disrupt the developing neurosensory appendages of the cricket and the imaginal discs of Drosophila.

Animals↗
PubMed1981

Solution conformation of gramicidin S: An intramolecular nuclear Overhauser effect study.

The solution conformation of gramicidin S in deuterated dimethyl sulfoxide was investigated by using the intramolecular nuclear Overhauser effect experiment. Experimental Overhauser enhancements were compared with predicted values for each of the nine most-stable conformations (M1-M9) calculated by Dygert et al. on the basis of energy-minimization procedures [Dygert, M., Gō, N. & Scheraga, H. A. (1975) Macromolecules 8, 750-761]. By using statistical hypothesis testing, the three lowest-energy conformations (M1, M2, and M3) were shown to give the best fit with the experimental data. All other conformations (M4-M9) were found to be inconsistent with the experimental data.

Journal Article↗
PubMed1981

H N.M.R. study of the conformation of [Glu4] oxytocin and its lanthanide complexes in aqueous solution.

At 400 MHz the 1H chemical shifts, peptide NH-C alpha H coupling constants (JN alpha) and peptide hydrogen exchange rates of [Glu4] oxytocin in aqueous solution closely resemble those previously reported for oxytocin under comparable conditions, indicating that both the parent hormone and its analogue have similar conformations in this solvent. The hydrogen exchange data suggest a dynamic equilibrium between conformation(s) in which the peptide NH's of Asn5 and Cys6 are internally hydrogen bonded and conformation(s) in which these hydrogens are bonded to the solvent. [Glu4] oxytocin forms 1:1 complexes with lanthanide metal ions. The diamagnetic La3+ complex exhibits values of JN alpha very similar to those of the metal free hormone analogue, suggesting that coordination of the metal is accompanied by minimal perturbation of the peptide backbone. Specific average proton-metal distances estimated from Gd3+ induced paramagnetic relaxation effects indicate that the metal is probably coordinated to the Glu4 carboxyl group and the sidechain carbonyl of Asn5. Limiting shifts induced by binding of paramagnetic Yb3+ are also reported.

Hydrogen Bonding↗
PubMed1981

[A two-stage technique for concentration of viruses from solutions with low virus titers (e.g., drinking water)].

The evidence of viruses in drinking water is an important component of studies of viruscirculation between man and his environment. In the two-stage concentration technique presented in this paper the method of aluminium sulphat flocculation, verified in more than 1300 investigations, is the first stage. In the second stage, aluminium hydroxide gel is at first dissolved with 1 ml of citric acid sodium citrate buffer at pH 4,7. The physico-chemical aspects of the lysis are discussed. It is from the lysate, that is not toxic for viruses, that viruses are separated by ultracentrifugation and inoculated on cell cultures. Owing to considerable constriction effect of about 20 000:1 is the method especially suitable for evidence of viruses in solutions with low virus titers (e.g. drinking water) as confirmed by a series of tests.

Aluminum Hydroxide↗
PubMed1980

Proline specific endo- and exopeptidases.

Peptidases which are specific for proline residues have been described and include endopeptidases (post-proline cleaving enzyme and proline specific endopeptidase), N-terminal exopeptidases (post-proline dipeptidyl aminopeptidase, proline iminopeptidase, aminopeptidase P), C-terminal exopeptidases (prolylcarboxypeptidase, and carboxypeptidase P) and dipeptidases (prolyl dipeptidase and proline dipeptidase). The properties, distinguishing charcteristics, and possible significance of these proline specific endo- and exopeptidases are discussed. In addition, reference is made to a series of enzymes which can hydrolyze proline containing peptide bonds, but which are not specific for proline.

Aminopeptidases↗