Holger Martens

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Urea transport across the gastrointestinal tract involves transporters of the urea transporter-B group, the regulation of which is poorly understood. The classical stimulatory effect of CO(2) and the effect of short-chain fatty acids (SCFA) on the ruminal recycling of urea were investigated by using Ussing chamber and microelectrode techniques with isolated(More)
Unidirectional 22Na+ and 36Cl− fluxes were determined in short-circuited, stripped rumen mucosa from sheep by using the Ussing chamber technique. In both CO2/HCO − 3 -containing and CO2/HCO − 3 -free solutions, replacement of gluconate by short-chain fatty acids (SCFA, 39 mM) significantly enhanced mucosal-toserosal Na+ absorption without affecting the Cl−(More)
In goats and other ruminants, urea functions as a source of nitrogen for protein biosynthesis in the digestive tract. Ammonia can be absorbed in the digestive system when formed in excessive quantitites and enhance formation of urea, or it can be derived from urea of blood plasma when its formation from feed sources is small. Entry rates of urea into plasma(More)
Influences of short-chain fatty acids (SCFA), chloride or lactate on net bicarbonate movement were determined in the temporarily isolated and washed reticulo-rumen of sheep used to 100% hay or 81% concentrate diets. Replacement of SCFA by gluconate and mannitol reversed net bicarbonate secretion into net absorption. The reversal of net bicarbonate movement(More)
Rumen: 1. It is generally accepted that sodium and chloride is transported across the rumen epithelium of ruminants in the mucosal-serosal direction by an active transport mechanism. In all in vitro studies the short circuit current, Isc, was significantly lower than the net transport of sodium, JNanet. It was concluded that most of the sodium is(More)
Ruminal epithelium adapts to dietary change with well-coordinated alterations in metabolism, proliferation, and permeability. To further understand the molecular events controlling diet effects, the aim of this study was to evaluate protein expression patterns of ruminal epithelium in response to various feeding regimes. Sheep were fed with a(More)
The absorption of short-chain fatty acids (SCFA) from the rumen requires efficient mechanisms for both apical uptake and basolateral extrusion. Previous studies suggest that the rumen expresses a basolateral chloride conductance that might be permeable to SCFA. In order to characterize this conductance in more detail, isolated cultured ruminal epithelial(More)
Net Mg(2+) absorption from the rumen is mainly mediated by a transcellular pathway, with the greater part (62%) being electrically silent. To investigate this component of Mg(2+) transport, experiments were performed with isolated ruminal epithelial cells (REC). Using the fluorescent indicators mag-fura 2, sodium-binding benzofuran isophthalate, and 2',(More)
We hypothesized that the decrease in the absolute amount of Mg absorbed in the total digestive tract, as induced by K, would remain constant if Mg intake by ruminants was increased. This hypothesis was based on earlier studies that used temporarily isolated rumens of sheep and the fact that the rumen is the major site of Mg absorption in ruminants. To test(More)
We have studied the transport of acetate across the isolated epithelium of sheep omasum; no net transport was observed (J ms ≈ 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 (r 2=0.99) with the luminal acetate concentration. The(More)