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Biomedical subjects

S Løvtrup

Publications and source records attributed to S Løvtrup.

At least 19 recordsLinked to original sources
PubMed1992

Biodynamics of living cells: the molecule-contraction theory.

Living cells can carry out work, by transforming chemical to mechanical energy. It has been found that such biodynamic activities are carried out by filaments built of proteinaceous subunits. Since work in general involves contractions, the proteins which are involved in the execution of work may thus be called "contractile proteins". There seem to be three such proteins: flagellin, actin and tubulin, forming bacterial flagella, actin filaments and microtubules, respectively. Myosin is also a filament-forming protein, important for the activity of actin filaments, notably in striated muscle cells, but it is not a contractile protein. When a muscle works, that is, contracts, then it is observed that the actin filaments slide in between the myosin filaments, and this observation has been used to develop a theory of contraction, the "sliding filament" theory. But it should be emphasized that this theory is essentially descriptive, not explanatory, and the main point in muscular activity, the presence of two kinds of filament, is not found in most other cases when cells are performing physical work. In order to solve this dilemma and reach a general theory of biodynamics the molecule-contraction theory, as presented here and on some earlier occasions, was created. The essential aspect of the theory is the existence of "contractile" proteins, which also have the property of forming filaments. This theory is based on four premises, out of which three are supposed to be involved in all kinds of biodynamic activity, while the fourth is required only in those instances where polymerization and depolymerization is a constituent part of the performance of mechanical work.

Amphibians↗
PubMed1990

Development of chicken embryos in a pulsed magnetic field.

Six independent experiments of common design were performed in laboratories in Canada, Spain, Sweden, and the United States of America. Fertilized eggs of domestic chickens were incubated as controls or in a pulsed magnetic field (PMF); embryos were then examined for developmental anomalies. Identical equipment in each laboratory consisted of two incubators, each containing a Helmholtz coil and electronic devices to develop, control, and monitor the pulsed field and to monitor temperature, relative humidity, and vibrations. A unipolar, pulsed, magnetic field (500-microseconds pulse duration, 100 pulses per s, 1-microT peak density, and 2-microseconds rise and fall time) was applied to experimental eggs during 48 h of incubation. In each laboratory, ten eggs were simultaneously sham exposed in a control incubator (pulse generator not activated) while the PMF was applied to ten eggs in the other incubator. The procedure was repeated ten times in each laboratory, and incubators were alternately used as a control device or as an active source of the PMF. After a 48-h exposure, the eggs were evaluated for fertility. All embryos were then assayed in the blind for development, morphology, and stage of maturity. In five of six laboratories, more exposed embryos exhibited structural anomalies than did controls, although putatively significant differences were observed in only two laboratories (two-tailed Ps of .03 and less than .001), and the significance of the difference in a third laboratory was only marginal (two-tailed P = .08). When the data from all six laboratories are pooled, the difference in incidence of abnormalities in PMF-exposed embryos (approximately 25 percent) and that of controls (approximately 19 percent), although small, is highly significant, as is the interaction between incidence of abnormalities and laboratory site (both Ps less than .001). The factor or factors responsible for the marked variability of inter-laboratory differences are unknown.

Animals↗
PubMed1988

The morphogenesis of molluscan shells: a mathematical account using biological parameters.

In attempts to account mathematically for the morphogenesis of biological structures it is important that the parameters chosen for the purpose should be "biological," that is, they should refer directly to the growth processes through which the structure is formed. Molluscan shells are formed by accretional growth at the mantle edge, and the parameters used for the mathematical description of their formation should therefore refer to events taking place there. In the best of previous attempts to solve this problem, two out of three form parameters have met with this demand, but it was not possible to eliminate beta, half the apical angle of the cone on which lie the centers of successive whorls. It is shown here that beta may be eliminated for many forms of molluscan shells, and when this is not the case beta may indeed be referred to processes taking place at the mantle edge.

Animals↗
PubMed1988

Factors involved in the formation and stabilization of cell aggregates obtained from amphibian embryonic explants.

The effect of factors influencing the formation and stability of animal and vegetal aggregates from Xenopus laevis and Ambystoma mexicanum was examined in the light and scanning electron microscopes. At extreme values of pH the surface coat covering the vegetal aggregates is dissolved and dissociation may take place. Animal aggregates are more resistant. At high tonicities vegetal aggregates may be dissociated, and in the animal aggregates the epidermal differentiation is suppressed. In the absence of Ca2+ the vegetal aggregates are dissociated, but the animal aggregates are not affected. The results obtained with the inhibitor selenate and from incorporation experiments indicate that sulfated glycosaminoglycans are involved in the formation of aggregates in both species. Corresponding observations with tunicamycin suggest that even glycoproteins may play a role in aggregate formation, particularly in the vegetal aggregates.

Ambystoma↗
PubMed1987

Autoneuralization in the amphibian ectoderm--a species-specific and stage-specific phenomenon.

Ectoderm from Ambystoma is especially prone to undergo 'autoneuralization'. This assertion has led to the maxim that ectoderm from this species is unsuitable for studying cell differentiation. Here we report that the degree of neuralization in cultured explants is stage-dependent. Control explants from blastulae (stage 8-9) show no neuralization, while explants treated with LiCl (10 mM) give rise to neuralization in about 70% of the cases. This difference between control and experiment decreases during gastrulation, in late gastrulae (stage 12) it is more or less negligible. Ectoderm from Cynops pyrrhogaster reacts like that of Ambystoma when exposed to LiCl, but like Triturus ectoderm it is insensitive to cyclic nucleotides.

Ambystoma↗
PubMed1986

Cyclic AMP and cell differentiation in amphibian embryonic explants.

Conflicting results have been published concerning the effects of cyclic nucleotides on amphibian cell differentiation. Here we report the effects of cyclic adenosine monophosphate (cAMP) and dibutyryl-cyclic adenosine monophosphate (db-cAMP) on isolated explants from late blastulae of Ambystoma mexicanum and Xenopus laevis. Both cAMP and db-cAMP (10(-4)-10(-9) M) promote 'neuralizing' differentiation in Ambystoma explants. Xenopus explants treated with the nucleotides (10(-4), 10(-6), 10(-8) M) LiCl or heparan sulphate only give rise to ciliated aggregates or dissociation. The results confirm observations that different amphibian species react in different ways to activating chemicals.

Ambystoma↗
PubMed1985

Effects of protracted exposure to low intensity radio frequency fields on CHO cells in culture.

This study was performed in order to investigate the biological effects of chronic exposure to low intensity radio frequency fields. By using CHO cells in culture, it was possible to extend exposure to several cell generations. The RF field consisted of a 27 MHz magnetic field (6 A/m), which produces a specific absorption rate of 1 W/kg. Exposure was continued for two to five days. The cells were then studied with respect to certain cell biological parameters: vital staining, plating efficiency, growth rate, volume and physical properties of the intracellular water, as measured by NMR. Scanning electron microscopy studies were also performed. A significant difference between exposed and control cells was found only with respect to intracellular water. A 10% decrease in line width which may indicate a corresponding increase in the spin-spin relaxation time was noted after exposure. A change in the colony forming pattern was also observed in thin cultures after two days of exposure.

Animals↗
PubMed1984

Sulfated polysaccharides and cell differentiation in the sea urchin embryo.

The synthesis of sulfated polysaccharides during the embryonic development of Paracentrotus lividus has been investigated by incorporation of radioactive sulfate, glucose, glucosamine and fucose. The following substances become labelled: fucan sulfate (approximately 60%), heparan sulfate (approximately 20%) and dermatan sulfate (approximately 20%), and possibly a very slight amount of chondroitin sulfate. In animalized and vegetalized embryos, the rate of incorporation is significantly reduced, and furthermore dermatan sulfate is almost absent in animalized embryos. It is concluded that this substance is associated with the differentiation of vegetative cells, possibly the mesenchyme cells.

Animals↗
PubMed1983

DNA concentrations in the human cerebellum. Computation from kinetics of deoxyribose extraction in hot acid.

DNA can be measured in mammalian tissues by extracting deoxyribose from unfixed, lyophilized tissue specimens with 0.5 N perchloric acid at 90 degrees C. Deoxyribose concentrations in the extract are determined photometrically by reaction with diphenylamine. Inevitably, some deoxyribose is destroyed during exposure to the hot acid. A computer program has been written which corrects photometric absorbance data for such loss of deoxyribose. When extrapolated to infinite duration of extraction, the corrected absorbances yield a measure of the DNA content of the specimen. This method was used to estimate DNA concentrations in human cerebellar cortex and white matter. The results are discussed in relation to stable carbon isotope ratios of human cerebellar DNA.

Cerebellar Cortex↗
PubMed1982

Cell physiological effects of radiofrequency electromagnetic fields.

Ovarian and body cavity eggs from R. temporaria were exposed to radiofrequency (rf) electromagnetic fields in the frequency range 10-27 MHz with specific absorption rates (SAR) up to 800 W/kg. The effect of the exposure was investigated by measurement of the water-related cell physiological parameters, isotopic and osmotic water membrane permeability and density of the egg cells. Only the osmotic water permeability, Pf, of ovarian eggs was significantly altered. A decrease of about 30% was seen for SARs of 50 W/kg and exposure times up to 2 h. Tests ruled out that the effect was due to temperature increase during the exposure. The observed decrease of Pf was most likely due to cloudy swelling of the egg cytoplasm resulting from the rf irradiation.

Animals↗