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Biomedical subjects

E B Jensen

Publications and source records attributed to E B Jensen.

At least 19 recordsLinked to original sources
PubMed2000

Non-uniform systematic sampling in stereology.

Non-uniform systematic sampling designs in stereology are studied. Various methods of constructing non-uniform systematic sampling points from prior knowledge of the measurement function are presented. As an example, we consider area estimation from lengths of linear intercepts. The efficiency of two area estimators, based on non-uniform sampling of parallel lines, is compared to that of the classical 2D Cavalieri estimator, based on uniform sampling, in a sample of planar profiles from transverse sections of 41 small myelinated axons. The comparison is based on simulations. It is concluded that for profiles of this type one of the non-uniform sampling schemes is more efficient than the traditional uniform sampling scheme. Other examples where non-uniform systematic sampling may be used are in area estimation from lines emanating from a fixed point, area estimation from concentric circles or spirals and curve length estimation from sweeping lines. It is shown that proportional-to-size sampling is a special case of non-uniform systematic sampling. Finally, the effect of noise in the observations is discussed.

Axons↗
PubMed2000

Activation of AMP-activated protein kinase increases mitochondrial enzymes in skeletal muscle.

Muscle contraction causes an increase in activity of 5'-AMP-activated protein kinase (AMPK). This study was designed to determine whether chronic chemical activation of AMPK will increase mitochondrial enzymes, GLUT-4, and hexokinase in different types of skeletal muscle of resting rats. In acute studies, rats were subcutaneously injected with either 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR; 1 mg/g body wt) in 0.9% NaCl or with 0.9% NaCl alone and were then anesthetized for collection and freezing of tissues. AMPK activity increased in the superficial, white region of the quadriceps and in soleus muscles but not in the deep, red region of the quadriceps muscle. Acetyl-CoA carboxylase (ACC) activity, a target for AMPK, decreased in all three muscle types in response to AICAR injection but was lowest in the white quadriceps. In rats given daily, 1 mg/g body wt, subcutaneous injections of AICAR for 4 wk, activities of citrate synthase, succinate dehydrogenase, and malate dehydrogenase were increased in white quadriceps and soleus but not in red quadriceps. Cytochrome c and delta-aminolevulinic acid synthase levels were increased in white, but not red, quadriceps. Carnitine palmitoyl-transferase and hydroxy-acyl-CoA dehydrogenase were not significantly increased. Hexokinase was markedly increased in all three muscles, and GLUT-4 was increased in red and white quadriceps. These results suggest that chronic AMPK activation may mediate the effects of muscle contraction on some, but not all, biochemical adaptations of muscle to endurance exercise training.

Adaptation, Physiological↗
PubMed1999

The efficiency of systematic sampling in stereology--reconsidered.

In the present paper, we summarize and further develop recent reseach in the estimation of the variance of sterelogical estimators based on systematic sampling. In particular, it is emphasized that the relevant estimation procedure depends on the sampling density. The validity of the variance estimation is examined in a collection of data sets, obtained by systematic sampling. Practical recommendations are also provided in a separate section.

Analysis of Variance↗
PubMed1997

The optical rotator.

The optical rotator is an unbiased, local stereological principle for estimation of cell volume and cell surface area in thick, transparent slabs. The underlying principle was first described in 1993 by Kiêu & Jensen (J. Microsc. 170, 45-51) who also derived an estimator of length. In this study we further discuss the methods derived from this principle and present two new local volume estimators. The optical rotator benefits from information obtained in all three dimensions in thick sections but avoids over-/ underprojection problems at the extremes of the cell. Using computer-assisted microscopes the extra measurements demand minimal extra effort and make this estimator even more efficient when it comes to estimation of individual cell size than many of the previous local estimators. We demonstrate the principle of the optical rotator in an example (the cells in the dorsal root ganglion of the rat), evaluate its efficiency and compare it with other unbiased, local stereological principles available for estimation of cell volume and surface area.

Animals↗
PubMed1995

Fusarium graminearum A 3/5 as a novel host for heterologous protein production.

We describe a novel fungal expression system which utilizes the Quorn myco-protein fungus Fusarium graminearum A 3/5. A transformation system was developed for F. graminearum and was used to introduce the coding and regulatory regions of a trypsin gene from Fusarium oxysporum. The protein was efficiently expressed, processed and secreted by the recombinant host strain. In addition, the promoter and terminator of the F. oxysporum trypsin gene have been successfully utilized to drive the expression of a cellulase gene from Scytalidium thermophilum and a lipase gene from Thermomyces lanuginosus in F. graminearum.

Base Sequence↗
PubMed1992

Characterization of tertiary interactions in a folded protein by NMR methods: studies of pH-induced structural changes in human growth hormone.

The pH-induced conformational changes in human growth hormone (hGH) have been studied, using a new quantitative NMR approach that combines 13C labeling of specific backbone carbonyl carbons with a complete spectral analysis of the corresponding 13C resonances. Thus, a complete analysis of the carbonyl resonances of the 26 Leu residues of hGH and their variation with pH provided detailed information about the equilibrium folding processes of the protein, including information about the kinetics of the folding. By combining this information with the pH dependence of readily identifiable 1H resonances, the pH-induced changes observed in the carbonyl carbon spectra can be associated with specific regions in the protein and can be ascribed to a series of localized adjustments in the tertiary structure, brought about by changes in the hydrogen bond interactions or electrostatic interactions between different residues in the globular folded protein. The preexchange lifetimes of these adjustments range from a fraction of a millisecond to a few milliseconds.

Amino Acid Sequence↗
PubMed1992

Specific carbon-13 labelling of leucine residues in human growth hormone.

Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized.

Carbon Isotopes↗
PubMed1990

Estimation of structural anisotropy based on volume orientation. A new concept.

The quantification of anisotropy--its main direction and the degree of dispersion around it--is desirable in numerous research fields dealing with physical structures. Conventional methods are based on the orientation of interface elements. The results of these methods do not always agree with perceived anisotropy, and anisotropic structures do not necessarily turn out to be 'anisotropic' using these methods. In the present paper, we propose an alternative to curve and surface orientation, namely volume orientation. Using trabecular bone as an example of a two-phase anisotropic structure, the new concept is studied in some detail. In particular, a parametric method of estimating volume orientation from sections is presented and discussed.

Adult↗
PubMed1989

High-level expression of active human cystatin C in Escherichia coli.

Expression of the human cysteine proteinase inhibitor, cystatin C (CysC) in the cytoplasm of Escherichia coli was studied using a cDNA fragment encoding the cysteine proteinase inhibitor controlled by the phage lambda pR/cI857 system. The yield of CysC was low, probably due to proteolytic degradation. By fusing the cysC cDNA to a DNA fragment encoding the signal peptide of the E. coli outer membrane protein A, it was possible to produce a substantial amount of CysC in the periplasm. The processing of the signal peptide was shown to be quantitative and to result in CysC with the correct N-terminal amino acid. Yields higher than 1000 micrograms CysC/ml can be obtained by initiating the product formation at a moderate temperature (40 degrees C) late in an optimized fermentation process. A method that gives selective extraction of the periplasmic proteins and at the same time stabilizes CysC has been used.

Bacteriophage lambda↗
PubMed1989

Plasma desorption mass spectrometry, an analytical tool in protein engineering: characterization of modified insulins.

Californium-252 plasma desorption mass spectrometry (PDMS) has been employed for the characterization of a series of human insulin derivatives in order to evaluate the performance of this technique as an analytical tool in protein engineering. Several of the characterized modifications result in a 1 a.m.u. mass change. The precision in mass determination obtainable by PDMS analysis is not sufficient for unambiguous verification of such modifications based on the molecular weight alone. It is, however, possible to carry out in situ enzymatic digestion of the sample. Subsequent PDMS analysis will in most cases reveal if the modification has been introduced as intended.

Amino Acid Sequence↗
PubMed1987

The efficiency of systematic sampling in stereology and its prediction.

The superior efficiency of systematic sampling at all levels in stereological studies is emphasized and various commonly used ways of implementing it are briefly described. Summarizing recent theoretical and experimental studies a set of very simple estimators of efficiency are presented and illustrated with a variety of biological examples. In particular, a nomogram for predicting the necessary number of points when performing point counting is provided. The very efficient and simple unbiased estimator of the volume of an arbitrary object based on Cavalieri's principle is dealt with in some detail. The efficiency of the systematic fractionating of an object is also illustrated.

Animals↗
PubMed1985

Stereological estimation of the volume-weighted mean volume of arbitrary particles observed on random sections.

A stereological estimator of the weighted mean volume of particles of arbitrary shape is described. This unbiased estimator is based on simple point-sampling of linear intercept lengths. The complete absence of shape assumptions effectively breaks the long-standing 'convexity-barrier': the only requirement here is that individual particles can be unambiguously identified by their profiles on random sections. Practical details of the simple estimation procedure and an example with very irregular particles are reported. Finally, an estimator of the variance of the weighted distribution of particle volume is discussed. This estimator is also valid for particles of arbitrary shape. For any mixture of ellipsoids (spheres, oblates, prolates and triaxial ellipsoids) the estimator is reduced to a simple function of measurements of diameters in the section plane.

Animals↗
PubMed1984

Is 'schizophrenia, schizo-affective type' a useful diagnosis? Ten years experience from Danish psychiatric hospitals.

During the period 1 April 1970 to 31 March 1980, 1,039 admissions (592 males and 447 females) with the main diagnosis schizophrenia, schizo-affective type, were registered in Danish psychiatric hospitals. Based on the Danish Central Psychiatric Register, 114 patients first admitted to psychiatric hospitals in the period 1970 to 1978 with the main diagnosis schizophrenia, schizo-affective type in at least one admission are described. The results show a continued increase in the use of the diagnosis, but the variation in the use both in different psychiatric hospitals and in patients' admission histories is striking. The question, whether the diagnosis is useful in this way, is discussed, and a proposal for a different international classification of schizo-affective psychoses is given.

Adolescent↗
PubMed1983

The binding of thiopental to human serum albumin at variable pH and temperature.

The binding of thiopental was studied in vitro by equilibrium dialysis over the concentration range 0.8-80 micrograms/ml in solutions with 45 g albumin (HSA) per litre. The binding at 37 degrees was from 79% to 67.6% at pH 6 while it was 94.5% to 93.0% at pH 9. At intermediate values of pH the observed values for binding were compatible with the assumption of a gradual transition of an N-form of HSA present exclusively at pH 6 to a B-form present exclusively at pH 9. The variation in binding could not be explained by changes in the balance between ionised and nonionized drug (pKa = 7.6). An increase in r (number of thiopental molecules bound per HSA molecule) was demonstrated when the temperature was lowered to 2 degrees. Graphs showing the relation between drug concentrations and percentual binding all showed a very modest slope and it was concluded that a traditional binding model with calculation of the number of binding sites and association constants was of little use in the evaluation of our binding studies of thiopental. The binding between thiopental and albumin may be characterized best by the solubility of thiopental in hydrophobic areas in the albumin solutions.

Humans↗
PubMed1980

The binding of thiopental to serum proteins determined by ultrafiltration and equilibrium dialysis.

An ultrafiltration method is described by which it is possible to estimate the protein bound fraction of a drug at its original concentration in a serum sample. The determination is carried out at 37 degrees and pH 7.4. For thiopental no difference was found between the values of protein binding whether they were determined by the ultrafiltration method or by a less time consuming equilibrium dialysis against an equal volume of phosphate buffered isotonic sodium chloride solution. The equilibrium dialysis was used to measure the concentration of bound and unbound thiopental molecules and the binding parameters in a two class binding model were determined. No evidence was found for binding to other proteins than albumin. About one binding site belonging to the first class was found per 1000 albumin molecules whereas an average of about 5 secondary sites were found for each albumin molecule. The association constants for the primary class of binding sites were 3.4 X 10(6)M-1 for albumin and 13.3 X 10(6)M-1 for serum while the values for the secondary class were 2.2 and 1.2 X 10(3)M-1 for albumin and serum respectively. The estimates of association constants and number of binding sites were based on experiments with total thiopental concentrations ranging from 0.4 to 80 microgram/ml. In a phosphate buffered albumin solution with 2 g albumin per 100 ml, a pH increase from 5 to 8 caused an increase in protein binding from 36 to 76%. A Scatchard plot using data from experiments with increasing albumin concentrations resulted in a "plot" with positive slope. The use of a curve like this is discussed and it is concluded that the binding parameters for thiopental are influenced by the albumin concentration.

Dialysis↗