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H Martens

Publications and source records attributed to H Martens.

At least 19 recordsLinked to original sources
PubMed2006

Transport of acetate and sodium in sheep omasum: mutual, but asymmetric interactions.

We have studied the transport of acetate across the isolated epithelium of sheep omasum; no net transport was observed (J(ms) approximately = J(sm)) under Ussing chamber conditions. Low mucosal pH (pH 6.4) significantly enhanced J(ms) acetate and the transport rates of acetate increased linearly and significantly (r2=0.99) with the luminal acetate concentration. The presence of another short chain fatty acid (propionate) did not affect J(ms) acetate significantly. Neither addition of 1 mmol l(-1) DIDS to the mucosal side nor HCO3 replacement caused changes of J(ms) acetate; this does not support the assumption of acetate transport via anion exchange. Addition of 1 mmol l(-1) amiloride to the mucosal side significantly decreased acetate fluxes at high mucosal acetate concentration (100 mmol l(-1)) and low pH (6.4) indicating interaction between acetate uptake in the undissociated form, intracellular release of protons and activation of Na+/H+ exchange (NHE). However, the mutual interaction between Na transport via NHE and acetate transport is asymmetric. Stimulation or inhibition of Na transport via NHE is much more pronounced than the corresponding changes of acetate fluxes. Thus, the obtained results support the conclusion that acetate is transported via simple diffusion and probably predominantly in the protonated form, thereby explaining the positive and mutual interaction between Na transport and short chain fatty acids.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2006

Physics-based multiplicative scatter correction approaches for improving the performance of calibration models.

Light scattering effects pose a major problem in the estimation of chemical properties of particulate systems such as blood, tissue, and pharmaceutical solids. Recently, Martens et al. proposed an extended multiplicative signal correction (EMSC) approach where light-scattering effects were taken into account in an empirical manner. It is possible to include causal, first-principles mathematical models based on the physics of light scattering into the EMSC framework. This could lead to significant improvements in the separation of absorption and scattering effects. A preconditioning step prior to application of EMSC, whereby a transformation based on the physics of light scattering is used to convert the spectra into a form where the absorption and scattering effects are separable (an underlying assumption of EMSC), is proposed. Results indicate that the transformation followed by EMSC gives better calibration models than the direct application of EMSC to the absorbance spectra.

Calibration↗
PubMed2005

Extended multiplicative signal correction as a tool for separation and characterization of physical and chemical information in Fourier transform infrared microscopy images of cryo-sections of beef loin.

Extended multiplicative signal correction (EMSC) is used to separate and to characterize physical and chemical information in spectra from Fourier transform infrared (FT-IR) microscopy. This appears especially useful for applications in infrared spectroscopy where the scatter variance in spectra changes with the chemical variance in the sample set. In these cases the chemical information of specific bands that are assigned to functional groups is easier to interpret when the scatter information is removed from the spectra. We show that scatter (physical) information in FT-IR spectra of heat-treated beef loin is related to chemical changes due to heat treatment. This information is caused by textural changes induced by the heat treatment and expressed by physical effects as the optical path length. The chemical absorbance changes introduced in the FT-IR spectra due to heat treatment are shifts in the protein region of the infrared spectrum caused by changes in the secondary structure of the proteins. If the scatter and the chemical information is not separated properly, scatter information may erroneously be interpreted as chemical information.

Algorithms↗
PubMed2004

Neurohypophysial receptor gene expression by thymic T cell subsets and thymic T cell lymphoma cell lines.

Neurohypophysial oxytocin (OT) and vasopressin (VP) genes are transcribed in thymic epithelium, while immature T lymphocytes express functional neurohypophysial receptors. Neurohypophysial receptors belong to the G protein-linked seven-transmembrane receptor superfamily and are encoded by four distinct genes, OTR, V1R, V2R and V3R. The objective of this study was to identify the nature of neurohypophysial receptor in thymic T cell subsets purified by immunomagnetic selection, as well as in murine thymic lymphoma cell lines RL12-NP and BW5147. OTR is transcribed in all thymic T cell subsets and T cell lines, while V3R transcription is restricted to CD4+CD8+ and CD8+ thymic cells. Neither V1R nor V2R transcripts are detected in any kind of T cells. The OTR protein was identified by immunocytochemistry on thymocytes freshly isolated from C57BL/6 mice. In murine fetal thymic organ cultures, a specific OTR antagonist does not modify the percentage of T cell subsets, but increases late T cell apoptosis further evidencing the involvement of OT/OTR signaling in the control of T cell proliferation and survival. According to these data, OTR and V3R are differentially expressed during T cell ontogeny. Moreover, the restriction of OTR transcription to T cell lines derived from thymic lymphomas may be important in the context of T cell leukemia pathogenesis and treatment.

Animals↗
PubMed2004

Sodium transport across the isolated epithelium of sheep omasum is influenced by luminal ammonia.

Ammonia is a physiological fermentation product in the forestomachs and is absorbed from the rumen and omasum. Cellular uptake of ammonia affects the intracellular pH of polar and non-polar cells. The effect of the uptake on the pH of the cytosol depends on the predominant form of ammonia. NH(3) uptake and its intracellular protonation tend to alkalinize the cytoplasm, whereas the uptake of NH(4)(+) acidifies the cytoplasm by reversing this reaction. Consequently, the absorption of ammonia across the omasal epithelium could cause a change of the intracellular pH and pH-dependent transport mechanisms like Na/H exchange. Because no information is available about the form of ammonia absorbed in the omasum and, hence, possible modulation of Na transport by ammonia, the effect of increasing luminal ammonia concentrations (0, 5, 15 and 30 mmol/l) on Na transport were studied. In epithelia of hay-fed animals, ammonia linearly inhibited Na transport in a dose-dependent manner, at a luminal pH of 7.40, but not at a pH of 6.40. Ammonia did not influence Na transport in epithelia of concentrate-fed animals. Because luminal ammonia did not consistently change the short circuit current or tissue conductance absorption of ammonia as NH(4)(+) appears to be unlikely. The predominant form of ammonia absorbed in the omasum is probably NH(3), which is protonated in the cytosol. The reduced availability of protons may be the cause of inhibition of Na transport via Na/H exchange.

Ammonia↗
PubMed2004

Resistance to barley scald (Rhynchosporium secalis) in the Ethiopian donor lines 'Steudelli' and 'Jet', analyzed by partial least squares regression and interval mapping.

The resistance of barley (Hordeum vulgare L.) to Rhynchosporium secalis (scald) has been investigated in two crosses between the susceptible cv. 'Ingrid' and two resistant Ethiopian landraces, 'Steudelli' and 'Jet'. Doubled haploids were inoculated in replicated tests using two isolates of R. secalis, '4004' and 'WRS1872'. Expression of resistance differed widely between replicated tests. AFLP, SSR and RFLP markers were used to develop chromosome maps. Results have been analysed using partial least squares regression (PLSR) and interval mapping. In PLSR the major covariance structures or 'latent variables' between X (markers) and Y (isolates, tests) are modelled as principal components and their optimal number determined by cross-validation. In 'Steudelli' two QTL were detected, one on each of chromosomes 3H and 7H, in 4 out of 5 tests, while in 'Jet' only one (different) allele at the 3H locus was found. The validated R(2) varied between 11.0% and 64.9% in the replicated tests with '4004'.With isolate 'WRS1872' the 7H locus and another 3H locus were detected. By interval mapping the QTL detected were less stable and generally gave lower R(2) values than PLSR. PLSR does not depend on maps, but interval mapping based on values predicted by PLSR had R(2) around 90%. It is suggested that PLSR may be a useful tool in QTL analysis.

Chromosome Mapping↗
PubMed2004

An insulin-like growth factor 2-derived self-antigen inducing a regulatory cytokine profile after presentation to peripheral blood mononuclear cells from DQ8+ type 1 diabetic adolescents: preliminary design of a thymus-based tolerogenic self-vaccination.

This work aims to evaluate the potential use of insulin-like growth factor 2 (IGF-2) as the dominant thymic self-antigen precursor of the insulin family in designing a tolerogenic approach to type 1 diabetes (T1D) prevention. This evaluation was primarily based on cytokine profile driven by MHC presentation of insulin and IGF-2-derived antigens to PBMC cultures derived from 16 T1D DQ8(+) adolescents. Insulin B9-23, one dominant beta-cell autoantigen, and the homologous sequence B11-25 of IGF-2 display the same affinity and fully compete for binding to DQ8, a MHC-II allele conferring major genetic susceptibility to type 1 diabetes (T1D). However, compared to insulin B9-23, presentation of IGF-2 B11-25 elicits a suppressive/regulatory cytokine profile with a higher number of IL-10-secreting cells (P < 0.05), a much higher ratio of IL-10/IFN-gamma (P < 0.01), as well as a lower number of IL-4-secreting cells (P < 0.05). Thus, with regard to T1D prevention, administration of IGF-2-derived self-antigen(s) seems to be an efficient approach that combines both antagonism for binding to a major susceptibility MHC-II allele, as well as downstream promotion of an antigen-driven tolerogenic response.

Adolescent↗
PubMed2004

[Discussion of a biometrical model for the evaluation of feeding, age, and animal effects on transport properties of small intestinal mucosa].

This paper is concerned with the question in which ways study results can depend on the choice of the statistical model and factors included in this model. This is shown using example data of a study dealing with the effects of an Enterococcus faecium as probiotic in the diet of pigs. We focused on the effects on transport properties of pig jejunum. The experimental design was the following: the sows and piglets were randomly assigned to two different feeding groups. The control group was fed a conventional diet and the experimental group was additionally supplemented with a probiotic preparation of Enterococcus faecium NCIMB 10415. The animals were divided into four age groups. Two samples of five animals of each feeding and age group were taken and mounted into conventional Ussing chambers. Glucose transport rates were measured by changes in short-circuit current (Isc) of the pig jejunum epithelium. The appropriate reference base for evaluation of effects of feeding or age on Isc is the variation between animals which are submitted to identical conditions relating to these factors. To refer explicitly to this variation a random animal effect has to be included in the statistical model of variance analysis. Otherwise the variation between animals could be underestimated. With the example data set conclusions for the factor "feeding" would be different depending on whether a random animal effect is included in the model or not.

Age Factors↗
PubMed2003

[Influence of potassium on Mg- and Ca-metabolism in cows: effects and side effects of scientific research].

Results of scientific studies are obtained by analysing of the present knowledge of a current problem and a corresponding new experimental set-up. Under ideal conditions the data of the new study agree with the deduced working hypothesis. This general consideration is true for the well established correlation between K content and growth rates of plants. At low K concentrations (up to 3% of dry matter) K causes a linear increase of growth and finally a saturation. This positive effect of K on growth rates of plants is accompanied by some side effects. There is no doubt that a high intake of K is involved in the pathogenesis of grass tetany and of milk fever. The present publication gives some information about this correlation and discusses the discrepancy between the intention of a scientific study and possible "side effects", which cannot be predicted in many cases.

Animal Feed↗
PubMed2003

The effect of short chain fatty acids on calcium flux rates across isolated rumen epithelium of hay-fed and concentrate-fed sheep.

The present in vitro experiment was conducted to study the effect of two concentrations of short chain fatty acids [SCFA: 0 (control), 40 and 100 mmol/l in the buffer solution on mucosal side] on calcium ion (Ca2+) transport across the isolated rumen epithelium of two groups of sheep. One group was subjected to hay ad libitum, whereas the other to concentrate feed (800 g per day in equal portion at 7.00 and 15.00 hours and hay ad lib). The conventional Ussing chamber method was used for measuring the Ca2+ transport rates (45Ca), short-circuit current (Isc) and tissue conductance (GT) of isolated rumen epithelium. The SCFA significantly increased Isc of the epithelia of concentrate-fed sheep. In both hay- and concentrate-fed animals, 45Ca flux rates showed an almost linear increase in net flux rate () with rising concentrations of SCFA, as a result of a combined effect of a large increase in mucosal-to-serosal flux rates () and an almost linear, but small, decrease in serosal-to-mucosal flux rate (). In concentrate-fed sheep and were significantly higher in tissues incubated with SCFA compared with hay-fed animals. The well-known adaptable morphological and functional changes in the rumen epithelium attributable to concentrate feeding obviously include Ca2+ transport; such feeding therefore may be considered as a possible prophylactic measure in the prevention of milk fever.

Adaptation, Physiological↗
PubMed2003

Modulation of Na+ transport across isolated rumen epithelium by short-chain fatty acids in hay- and concentrate-fed sheep.

The effect of increasing concentrations of short-chain fatty acids [SCFA; mixture of the Na+ salts of acetic acid (62.5%), propionic acid (25.0%) and of butyric acid (12.5%)] on Na+ transport of sheep rumen epithelium was studied in vitro. The conventional Ussing chamber method was used for measuring Na+ transport rates (22Na+), short-circuit current (Isc) and tissue conductance (GT) of isolated rumen epithelium. SCFA in the buffer solution on the mucosal side caused a linear increase of Jnet Na+ from 1.14, to 1.22, 1.78 and 2.50 microeq/cm2/h in hay-fed sheep at 0, 15, 40 and 80 mmol/l SCFA, respectively. In a second study, the effect of higher SCFA concentrations [0 (control), 80, 100 and 120 mmol/l] was investigated with epithelia from two groups of sheep. One group was subjected to hay ad libitum, whereas the other received concentrate feed (800 g/day in equal portions at 7.00 am and 3.00 pm) and hay ad libitum. Epithelia from concentrate-fed sheep again showed a significant (p < 0.05) and linear increase in Jnet Na+ at 80, 100 and 120 mmol/l. However, in hay-fed sheep, the difference in increase among 80, 100 and 120 mmol/l SCFA was not significant, indicating that, above 80 mmol/l SCFA Jms and Jnet exhibit saturation. Moreover, Na+ fluxes (Jms and Jnet) were generally higher in concentrate-fed than in hay-fed sheep at all SCFA concentrations and significant differences were observed at 100 and 120 mmol/l SCFA. The obtained results confirm the effect of SCFA on Na+ transport and are in agreement with studies regarding feeding regimes and electrolyte transport in the rumen. The important new observation is the increase of Na+ transport in concentrate-fed sheep even at high concentrations of SCFA (100 and 120 mmol/l). The enhanced activity of the Na+/H+ exchanger at these SCFA concentrations supports the assumption that the capacity for regulating the intracellular pH by extrusion of protons is increased, suggesting an adaptation in concentrate-fed sheep. This adaptation could prevent possible disturbances of epithelial functions (transport and barrier) under conditions of increased SCFA absorption.

Absorption↗
PubMed2003

Quantification of T cell receptor rearrangement excision circles to estimate thymic function: an important new tool for endocrine-immune physiology.

Although the thymus constitutes a target organ for most protein and steroid hormones, it has been quite difficult to determine the precise control exerted in vivo by the endocrine system upon thymic function. The biological role of the thymus is to ensure the generation of a diversified population of peripheral T cells able to respond to non-self-antigens but nevertheless tolerant to self-antigens. For a long time, thymic function could not be monitored, as a consequence of the absence of adequate technology to differentiate recent thymic emigrants from naive T cells. The generation of T cell receptor (TCR) diversity occurs in the thymus through recombination of gene segments encoding the variable parts of the TCR alpha and beta chains. During these processes, by-products of the rearrangements are generated in the form of TCR excision circles (TRECs). As these molecules are lost upon further cell division, their quantification is actually considered as a very valuable tool to estimate thymic function. The most appropriate TREC is deltaRec-Psi(J)alpha TREC or signal joint TREC resulting from deltaRec-Psi(J)alpha rearrangement (TCRD deletion) that occurs late during thymopoiesis, before V(alpha)-J(alpha) rearrangement. Here we describe how TREC quantification is a powerful and reliable method to evaluate the impact of hormones and endocrine disorders upon thymic function.

Aged↗
PubMed2002

[Influence of information campaigns on the vaccination immunity among the population of a small town area - seroepidemiological results of the 'Wittlich Vaccination Study'].

In the course of the three-phase 'Wittlich Vaccination Study' the population immunity against tetanus, diphtheria and poliomyelitis was controlled in all age groups of the regional population. Antibody measuring was done in specific validated enzyme immunoassays and neutralisation tests. After performing several campaigns for training and informing medical staff and the population about vaccinations the effect of these campaigns was checked in an additional control of the population immunity. The part of not or only partially protected participants decreased for tetanus from 36.7 % to 2.8 % and for diphtheria from 61 % to 51 %. The gap in population immunity was reduced for polio virus type 1 from 6.7 % to 3.1 %, for polio virus type 2 from 6.2 % to 2.5 % and for polio virus type 3 from 13.2 % to 3.6 %. The study design can be transferred to regions with comparable structure of their population.

Adolescent↗
PubMed2001

No evidence for active peptide transport in forestomach epithelia of sheep.

The transport of peptides was studied with isolated preparations of rumen and omasum tissue of sheep by using the conventional Ussing-chamber method and isolated ruminal cells (REC). Mucosal addition of glycyl-L-glutamine, captopril (angiotensin converting enzyme inhibitor) or cefadroxil (beta-lactam antibiotic) did not change the short-circuit current (I(sc)), or tissue conductance (G(t)). The intracellular pH, pH(i), in isolated REC was not influenced by the addition of peptides to the buffer solution. These findings do not support the assumption of proton-coupled or electrogenic peptide transport. The determination of unidirectional flux rates of the peptide D-phenylalanyl-L-alanine (2,3-(3)H) showed that the flux rate in the serosal-mucosal direction, J(sm), was greater than J(ms), leading to a small net secretion of peptide. Transport was not significantly inhibited by the serosal addition of ouabain. Enhancing the paracelluIar permeability by an increase of osmotic pressure in the mucosal solution (FREYER and MARTENS, Proc. Soc. Nutr. Physiol. 8, 80, 1999) caused an increase of G(t) and significantly higher transport rates of peptide. The flux rates of peptides (in the nanomolar range) may therefore represent passive and possibly paracellular diffusion and are not of nutritional importance.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2001

Millipedes and earthworms increase the decomposition rate of 15N-labelled winter rape litter in an arable field.

Effects of millipedes and earthworms on the decomposition of 15N-labelled litter of winter oilseed rape were investigated in a microcosm field experiment over a period of 264 days on an oat field near Göttingen managed by integrated farming. A total of 32 microcosms were filled with defaunated soil. 15N-labelled rape litter was placed either on top of the soil or buried into the soil simulating mulching and ploughing, respectively. To the microcosms nine adult individuals of Blaniulus guttulatus (Diplopoda) and two of Aporrectodea caliginosa (Lumbricidae) were added separately or in combination. In general, the presence of the animals accelerated the decomposition rate of the litter material. The effects were most pronounced in the presence of Aporrectodea caliginosa. The total amount of nitrate, ammonium and the amount of 35N leached from the microcosms was increased in the presence of earthworms or of both earthworms and millipedes. Both species proved to be important members of the detritus food web of the agricultural system studied.

Animals↗
PubMed2001

Dobrava hantavirus causes hemorrhagic fever with renal syndrome in central Europe and is carried by two different Apodemus mice species.

In central Europe, hemorrhagic fevers with renal syndrome (HFRS) in humans are caused by the hantavirus species Puumala (transmitted by voles) and a second, Hantaan-related species (transmitted by mice). The second virus could be identified as Dobrava virus. To date, 19 clinical cases of Dobrava infection have been found in Germany and Slovakia. All patients exhibited a mild/moderate clinical course and no case fatality occurred. Screening for infected rodents revealed that the striped field mouse (Apodemus agrarius) represents the main reservoir for Dobrava virus in central Europe. Nucleotide sequence comparisons and phylogenetic analysis based on complete and partial genomic S segment nucleotide sequences placed the Slovakian A. agrarius-derived hantavirus strains within the Dobrava species, forming a cluster on the Dobrava phylogenetic tree. In east Slovakia, a single Dobrava virus-infected yellow-necked mouse (Apodemus flavicollis) was trapped in a locality that predominantly showed Dobrava-infected A. agrarius. Comparison of the S segment sequence (nucleotides 381-935) revealed that the Dobrava strain from A. flavicollis shows only 84.3% nucleotide homology to A. agrarius-derived strains from this location but 96.3% homology to A. flavicollis-derived Dobrava strains from the Balkans (southeast Europe). Phylogenetic analysis of the partial S segment placed the A. flavicollis-derived Dobrava strain from Slovakia on a distinct Dobrava lineage (DOB-Af) together with the south-east European A. flavicollis-derived strains. The results indicate that Dobrava strains from A. agrarius (DOB-Aa) vs. A. flavicollis (DOB-Af) could develop different degrees of virulence in humans.

Adolescent↗
PubMed2001

Thymic T-cell tolerance of neuroendocrine functions: physiology and pathophysiology.

Intimate interactions between the two major systems of cell-to-cell communication, the neuroendocrine and immune systems, play a pivotal role in homeostasis and developmental biology. During phylogeny as well as during ontogeny, the molecular foundations of the neuroendocrine system emerge before the generation of diversity within the system of immune defenses. Before reacting against non-self infectious agents, the immune system has to be educated in order to tolerate the host molecular structure (self). The induction of self-tolerance is a multistep process that begins in the thymus during fetal ontogeny (central tolerance) and also involves anergizing mechanisms outside the thymus (peripheral tolerance). The thymus is the primary lymphoid organ implicated in the development of competent and self-tolerant T-cells. During ontogeny, T-cell progenitors originating from hemopoietic tissues (yolk sac, fetal liver, then bone marrow) enter the thymus and undergo a program of proliferation, T-cell receptor (TCR) gene rearrangement, maturation and selection. Intrathymic T-cell maturation proceeds through discrete stages that can be traced by analysis of their cluster differentiation (CD) surface antigens. It is well established that close interactions between thymocytes (pre-T-cells) and the thymic cellular environment are crucial both for T-cell development and for induction of central self-tolerance. Particular interest has focused on the ability of thymic stromal cells to synthesize polypeptides belonging to various neuroendocrine families. The thymic repertoire of neuroendocrine-related precursors recapitulates at the molecular level the dual role of the thymus in T-cell negative and positive selection. Thymic precursors not only constitute a source of growth factors for cryptocrine signaling between thymic stromal cells and pre-T-cells, but are also processed in a way that leads to the presentation of self-antigens by (or in association with) thymic major histocompatibility complex (MHC) proteins. Thymic neuroendocrine self-antigens usually correspond to peptide sequences highly conserved during the evolution of their corresponding family. The thymic presentation of some neuroendocrine self-antigens does not seem to be restricted by MHC alleles. Through the presentation of neuroendocrine self-antigens by thymic MHC proteins, the T-cell system might be educated to tolerate main hormone families. More and more recent experiments support the concept that a defect in thymic tolerogenic function is implicated as an important factor in the pathophysiology of autoimmunity.

Animals↗