In this study we investigated rumen papillae morphology and the localization and expression of the Na+/K+-ATPase in eight sheep fed hay ad libitum (h) or hay ad libitum plus additional concentrate (h/c). Four sheep were provided with the ad libitum h-diet for the complete three-week experimental period. The second group of four sheep received the h-diet for only one week and was fed the mixed hay/concentrate (h/c) diet for another two weeks. The amount of concentrate supplement was stepwise increased from 150 to 1000 g/day and given in two meals. Following slaughter rumen papillae from the atrium ruminis (AR), the rumen ventralis (RV) and the ventral blind sac (BSV) were fixed and examined for morphological changes and Na+/K+-ATPase localization by morphometric methods and immunohistochemistry. Ruminal epithelial cells (REC) originating from the strata basale to granulosum were also isolated. Cellular Na+/K+-ATPase expression (mRNA and protein) and differentiation state were determined by RT-PCR, Western blot, and flow cytometry. Compared with data from h-fed sheep, morphometric analysis revealed an increased length and width of rumen papillae in h/c-fed sheep, resulting in a marked 41% and 62% increase in rumen papillae surface in AR and RV, respectively. The rumen mucosa of h/c-fed sheep was characterized by a predominant stratum corneum (42 +/- 0.7 mu m vs. 28 +/- 0.5 mu m), but the thickness of the metabolically active cell layers remained unchanged. REC suspensions from sheep fed the h/c diet generally contained more cells (7.30 +/- 0.83 vs. 3.49 +/- 0.52 x 10(7)/ml; P < 0.001) and an increased proportion of REC positive for basal cytokeratin and for the differentiation marker cytokeratin 10 (P < 0.05). Cellular (cell membrane) and epithelial (stratum basale to stratum granulosum) Na+/K+-ATPase localization was similar between rumen regions and was not changed by concentrate feeding. After two weeks on the h/c-diet, a 96% increase in the absolute number of Na+/K+-ATPase-positive REC (6.56 +/- 0.84 vs. 3.35 +/- 0.51 x 10(7)/ml; P = 0.003) and a 61% elevation (P = 0.043) in Na+/K+-ATPase protein expression in REC from the upper third of the suprabasal cell layers were found. Moreover, a two-fold (P 0.001) elevation in cell membrane surface area accompanied by a reduction (1.19 x 10(-7) +/- 1.72 x 10(-9) arbitrary units (AU)/cm(2) vs. 1.73 x 10(-7) +/- 8.16 x 10(-9) AU/cm(2) in the h-group; P < 0.001) in specific Na+/K+-ATPase fluorescence per cm(2) of cell membrane surface area was observed after h/c-feeding. Na+/K+-ATPase a subunit mRNA expression was also reduced (P < 0.0001) from 0.154 +/- 0.013 to 0.057 +/- 0.004 pg per pg S18 mRNA control in the h/c-compared with the h-group. Thus, the h/c-diet led to a rapid increase in REC number and total cell membrane surface area in metabolically active and resorptive cell layers and was accompanied by a reduction in Na+/K+-ATPase mRNA expression and abundance per cell membrane surface area.

An open-circuit indirect calorimetry system consisting of 4 climate-controlled respiration chambers for cattle has been constructed and validated. The system allows for the continuous monitoring of O(2), CO(2), and CH(4) concentrations in chamber air, and the simultaneous determination of feed and water intake, overall physical activity, position changes, standing and lying times, and animal behavior. For complete balance trials, feces, urine, and milk can be collected quantitatively. Most importantly, lactating cows can be milked in the chamber, and blood samples can be drawn from permanent catheters without disruption of the measurements. The investigator, on entering the chamber, wears a facemask connected to the ambient air during the whole milking process. Data are routed to a data acquisition system with appropriate data evaluation software developed in our research unit. Thus, dynamic changes of the above-named parameters during the course of the day or of longer time periods can be monitored. Such data are critical for understanding the complex regulation and interplay of feed intake, energy metabolism, climatic conditions, and milk production.

Nine non-pregnant, lactating dairy cows were used to study plasma and urinary magnesium concentrations ([Mg]pl; [Mg]u), and the urinary fractional excretion of magnesium (FE(Mg)) before, during and after an 120 min intravenous magnesium (Mg) administration (2.5 mg/kg body weight). Animals received a total mixed ration, and Mg content of the diet was within recommended range. Basal mean [Mg]pl, [Mg]u and FE(Mg) were 0.89 +/- 0.09 mm, 5.92 +/- 2.99 mm and 8.3 +/- 9.7% respectively. For all parameters, a substantial inter-individual variation was observed. Three cows showed suboptimal [Mg]pl and/or [Mg]u as well as low FE(Mg) values of approximately 2% indicating an insufficient Mg supply to these animals (depressed feed intake, reduced absorption of Mg). The applied Mg challenge induced no significant change of mean [Mg]pl in the cows because part of the excess Mg was excreted in the urine. But in five out of nine cows, a decrease of the FE(Mg), during and after an intravenous Mg load was observed showing that part of the infused Mg is used to replenish intracellular Mg pools. Thus, the existence of an intracellular Mg deficiency in these cows was unmasked by performing the Mg loading test only. Because a reduced free intracellular [Mg] impairs cell and tissue functions, the results highlight the importance of an accurate definition of the intracellular Mg status. The Mg loading test is a suitable procedure, however, for practical purposes less expensive and time consuming methods must be developed.

An extensive number of investigations on the energetic utilization efficiency of nutrients and feedstuffs by cattle were carried out in the former Oskar-Kellner-Institute (now the »Oskar Kellner« Research Unit of Nutritional Physiology at the Research Institute for the Biology of Farm Animals (FBN), Dummerstorf ). The amounts of methane (CH4) that they produced were compiled and stratified with regard to various performances, dietary nutrient composition and nutrition levels. With increasing food intake and performance, an increase of CH4 emission per animal was observed. However, with increasing performance, a strong decrease of CH4 production per unit of product was determined. Altogether, the 12.74 million cattle in Germany produce 1.04 million tons of CH4 per year. This represents 1.25 % of the CH4 production of the 1.3 thousand million (UK)/billion (US) cattle in the world or 0.22 % of the total emission on the earth. As a greenhouse gas, CH4 from cattle worldwide and from cattle in Germany account for 3.5 % and 0.04 % of global warming, respectively. In addition, opportunities for a further reduction of enteric CH4 release are discussed.

The molecular biology of mammalian magnesium transporters and their interrelations in cellular magnesium homeostasis are largely unknown. Recently, the mouse SLC41A1 protein was suggested to be a candidate magnesium transporter with chan-nel-like properties when overexpressed in Xenopus laevis oocytes. Here, we demonstrate that human SLC41A1 overexpressed in HEK293 cells forms protein complexes and locates to the plasma membrane without, however, giving rise to any detectable magnesium currents during whole cell patch clamp experiments. Nevertheless, in a strain of Salmonella enterica exhibiting disruption of all three distinct magnesium transport systems (CorA, MgtA, and MgtB), overexpression of human SLC41A1 functionally substitutes these transporters and restores the growth of the mutant bacteria at

In this study data originating from complete metabolic trials with cattle of both sexes, fed 337 rations at feed intake levels between one to three times maintenance energy requirement were used to regress the total CH4 emission to the level of DM intake and to the nutrient composition, respectively. A major component of the measured CH4 emission cannot be explained by DM intake but is rather due to differences in dietary nutrient composition. The amount of digestible nutrients especially of the carbohydrate fraction (starch, sugar, N-free residuals) are reliable to estimate CH4 release with high precision (r2 = 0.885). Its production rate increased to 1.9-fold higher levels (range 1.8-2.1) per g of N-free residuals compared to that induced per g of protein, starch or sugar, respectively. Furthermore, diets rich in fat reduced CH4 formation in the rumen. The regression equations fit a wide range of diets and diet compositions, and more importantly, they are applicable to various types of production systems.

This study examines the routes by which Mg2+ leaves cultured ovine ruminal epithelial cells (REC). Mg2+-loaded (6 mM) REC were incubated in completely Mg2+-free solutions with varying Na+ concentrations, and the Mg2+ extrusion rate was calculated from the increase of the Mg2+ concentration in the incubation medium determined with the aid of the fluorescent probe mag-fura 2 (Na+ salt). In other experiments, REC were also studied for the intracellular free Mg2+ concentration ([Mg2+]i; using mag-fura 2), the intracellular Na+ concentration (using Na+-binding benzofuran isophthalate), the intracellular cAMP concentration ([cAMP]i; using an enzyme-linked immunoassay), and Na+/Mg2+ exchanger existence [using a monoclonal antibody (mAb) raised against the porcine red blood cell Na+/Mg2+ exchanger]. Mg2+-loaded REC show a Mg2+ efflux that was strictly dependent on extracellular Na+. The Mg2+ extrusion rate increased from 0.018+/-0.009 in a Na+-free medium to 0.73+/-0.3 mM.l cells-1.min-1 in a 145 mM Na+ medium and relates to extracellular Na+ concentration ([Na+]e) according to a typical saturation kinetic (Km value for [Na+]e=24 mM; maximal velocity=11 mM.l cells-1.min-1). Mg2+ efflux was reduced by imipramine (48%) and increased after application of dibutyryl-cAMP (55%) or PGE2 (17%). These effects are completely abolished in Na+-free media. Furthermore, an elevation of [cAMP]i led to an [Mg2+]i decrease that amounted to 375+/-105 microM. The anti-Na+/Mg2+ exchanger mAb inhibits Mg2+ extrusion; moreover, it detects a specific 70-kDa immunoreactive band in protein lysates of ovine REC. The data clearly demonstrate that a Na+/Mg2+ exchanger is existent in the cell membrane of REC. The transport protein is the main pathway (97%) for Mg2+ extrusion and can be assumed to play a considerable role in the process of Mg2+ absorption as well as the maintenance of the cellular Mg2+ homeodynamics.

This study aimed to test the hypothesis that maintenance energy requirement (MEm) can be estimated from continuous heat production measurements during a change from a near maintenance feeding level to far below maintenance for two consecutive days. The MEm of eight Hereford steers weighing 286 +/- 5 kg (mean +/- SE) was determined in a balance trial. In addition, during the 10-d collection period, the animals were kept in open-circuit respiration chambers to measure 24-h gas exchange continuously at 10-min intervals. During the balance trial, the animals were fed dried chopped grass twice daily at an estimated level of 1.2 x MEm. After termination of the collection period on the 11th d of the balance trial, the steers were offered 2 kg/d of wheat straw while only gas exchange was measured. Estimates of MEm were derived from heat production (HP) data. The analyses included values of 24-h HP, HP of the nocturnal period (0000 to 0630), HP of the nocturnal period (excluding HP caused by standing) during the grass-feeding period and 24-h HP, nocturnal HP, and nocturnal HP (excluding HP caused by standing) during the straw feeding period. The MEm predicted from estimates of HP measurements were 536 +/- 9, 470 +/- 8, 441 +/- 8, 435 +/- 8, 393 +/- 9, and 373 +/- 9 kJ.kg of BW(-0.75).d(-1), respectively, whereas MEm calculated from data of the balance trial were 416 +/- 9 kJ.kg of BW(-0.75).d(-1). Values predicted for nocturnal HP (excluding HP caused by standing) of grass fed animals, 24-h HP, and nocturnal HP during straw feeding did not differ significantly from MEm. The differences in MEm among animals were reflected by all estimates of HP, whereas the correlation with the 24-h HP during straw feeding reached 0.9 (P = 0.002). We conclude that the method described is adequate to determine MEm with a sufficient degree of accuracy.

The Mg2+ fluorescent dye mag-fura 2, entrapped in cells or organelles, has frequently been used for dual excitation ratio-metric determinations of free ionic Mg2+ concentrations in eukaryotic, mostly mammalian cells. Here we report its successful application to measure free Mg2+ concentrations ([Mg2+]i) in Salmonella enterica cells. When kept in nominally Mg2+ free buffer (resting conditions), the [Mg2+]i of wild-type cells has been determined to be 0.9 mM. An increase in the external Mg2+ concentration ([Mg2+]e) resulted in a rapid increase of [Mg2+]i, saturating within a few seconds at about 1.5 mM with [Mg2+]e of 20 mM. In contrast, cells lacking the Mg2+ transport proteins CorA, MgtA, MgtB failed to show this rapid increase. Instead, their [Mg2+]i increased steadily over extended periods of time and saturated at concentrations below those of wild-type cells. Mg2+ uptake rates increased more than 15-fold when corA was overexpressed in these mutant cells. Uptake of Mg2+ into corA expressing cells was strongly stimulated by nigericin, which increased the membrane potential DeltaPsi at the expense of DeltapH, and drastically reduced by valinomycin, which decreased the membrane potential DeltaPsi. These results reveal mag-fura 2 as a useful indicator to measure steady-state [Mg2+]i values in resting bacterial cells and to determine Mg2+ uptake rates. They confirm the role of CorA as the major Mg2+ transport protein and reveal the membrane potential as driving force for Mg2+ uptake into S. enterica cells.

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.

The K+-insensitive component of Mg2+ influx in primary culture of ruminal epithelial cells (REC) was examined by means of fluorescence techniques. The effects of extracellular anions, ruminal fermentation products, and transport inhibitors on the intracellular free Mg2+ concentration ([Mg2+]i), Mg2+ uptake, and intracellular pH were determined. Under control conditions (HEPES-buffered high-NaCl medium), the [Mg2+]i of REC increased from 0.56 +/- 0.14 to 0.76 +/- 0.06 mM, corresponding to a Mg2+ uptake rate of 15 microM/min. Exposure to butyrate did not affect Mg2+ uptake, but it was stimulated (by 84 +/- 19%) in the presence of CO2/HCO(-)3. In contrast, Mg2+ uptake was strongly diminished if REC were suspended in HCO(-)3-buffered high-KCl medium (22.3 +/- 4 microM/min) rather than in HEPES-buffered KCl medium (37.5 +/- 6 microM/min). After switching from high- to low-Cl- solution, [Mg2+]i was reduced from 0.64 +/- 0.09 to 0.32 +/- 0.16 mM and the CO2/HCO(-)3-stimulated Mg2+ uptake was completely inhibited. Bumetanide and furosemide blocked the rate of Mg2+ uptake by 64 and 40%, respectively. Specific blockers of vacuolar H+-ATPase reduced the [Mg2+]i (36%) and Mg2+ influx (38%) into REC. We interpret this data to mean that the K+-insensitive Mg2+ influx into REC is mediated by a cotransport of Mg2+ and Cl- and is energized by an H+-ATPase. The stimulation of Mg2+ transport by ruminal fermentation products may result from a modulation of the H+-ATPase activity.

Recently, most of the mobile network providers start to introduce general packet radio service (GPRS) in their existing GSM networks. GPRS is the technology that will enable more efficient Internet applications to run on mobile networks even before the installation of 3G systems. However, it is not yet clearly understood, how the new data services will affect the overall network performance. This paper provides a framework for analytical performance evaluation of a single GSM/GPRS cell based on a multidimensional Markov chain model. Important performance measures like new call and handover blocking probabilities, moments of the blocking period distributions, achievable average data rates and resource utilization are determined. Introducing a new connection admission control (CAC) algorithm, different partitioning strategies between GSM and GPRS resources are investigated. Finally, the influence of typical GPRS applications like Internet browsing on traditional GSM services has been studied.

Previous TCP performance investigations for wireless systems focus on TCP throughput degradation due to packet loss on the error-prone wireless link. Since cellular mobile networks like GPRS and UMTS include a strong link layer error protection, using adaptive Forward Error Correction and Automatic Repeat Request schemes, a bad quality of the wireless link does not mainly result in IP packet loss but rather in an additional packet delay. Furthermore TCP congestion control has to deal with hand-offs and temporary link layer disconnections in cellular mobile networks leading to a significant packet delay variation and packet disordering. This paper analyzes the performance of TCP in cellular mobile networks, focusing on the packet delay and disordering problem. We find spurious retransmissions and TCP timeouts being a dominant cause for throughput degradation. Finally we propose an algorithm to filter spurious TCP retransmissions at the Base Station to increase TCP performance and increase overall wireless link capacity.

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.