Mechanism of electrically silent Na and Cl transport across the rumen epithelium of sheep

Martens, H.; Gäbel, Gotthold; Strozyk, B

doi:10.1113/expphysiol.1991.sp003472

Cited by 47 publications

(68 citation statements)

References 34 publications

(76 reference statements)

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“…The pH i recovery rate is slightly higher in a medium with a reduced Cl Ϫ content. Although the reason for this effect has not been investigated in detail, it can be attributed to an inhibition of the activity of the HCO 3 Ϫ / Cl Ϫ exchanger, which is present in the cell membrane of REC (24). Such an effect has been described repeatedly in other cell systems (15,20) ] of 2 mM.…”

Section: Methodsmentioning

confidence: 96%

Anion-dependent Mg²⁺influx and a role for a vacuolar H⁺-ATPase in sheep ruminal epithelial cells

Schweigel

Martens

2003

American Journal of Physiology-Gastrointestinal and Liver Physi

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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 μM/min. Exposure to butyrate did not affect Mg2+ uptake, but it was stimulated (by 84 ± 19%) in the presence of [Formula: see text]. In contrast, Mg2+ uptake was strongly diminished if REC were suspended in [Formula: see text]-buffered high-KCl medium (22.3 ± 4 μM/min) rather than in HEPES-buffered KCl medium (37.5 ± 6 μM/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 [Formula: see text]-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.

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Section: Methodsmentioning

confidence: 96%

Anion-dependent Mg²⁺influx and a role for a vacuolar H⁺-ATPase in sheep ruminal epithelial cells

Schweigel

Martens

2003

American Journal of Physiology-Gastrointestinal and Liver Physi

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“…In vitro -in the absence of electrochemical gradients -chloride is absorbed across rumen epithelia, an absorption that depends on the presence of sodium, an active Na 1 /K 1 -ATPase and on the presence of bicarbonate (Chien and Stevens, 1972;Harrison et al, 1975;Martens et al, 1991). These dependencies have suggested the involvement of Cl 2 /HCO 3 2 exchangers coupled to NHE via intracellular pH in analogy to other epithelia of the gastrointestinal tract on the apical side (Figure 3).…”

Section: Absorption and Secretion Of Chloridementioning

confidence: 99%

“…1 absorption Ruminal electrogenic Na 1 transport differs from that of classical Na 1 absorbing epithelia, as it is not blocked by low doses of amiloride (,0.1 mmol/l; Martens et al, 1991), but varies with the luminal concentration of divalent cations (Figure 1). Both in the rumen and in the omasum, net Na 1 absorption and Isc as a measure of total electrogenic ion transport across a tissue are markedly increased when the mucosal concentrations of free divalent cations such as Ca 21 and Mg 21 are decreased (Leonhard et al, 1990;Rü bbelke, 1998;Schultheiss and Martens, 1999).…”

Section: Electrogenic Namentioning

confidence: 99%

Transport of cations and anions across forestomach epithelia: conclusions from in vitro studies

Leonhard-Marek

Stumpff

Martens

2010

Animal

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Secretion of saliva as well as absorptive and secretory processes across forestomach epithelia ensures an optimal environment for microbial digestion in the forestomachs. Daily salivary secretion of sodium (Na 1 ) exceeds the amount found in plasma by a factor of 2 to 3, while the secretion of bicarbonate (HCO 3 2 ) is 6 to 8 times higher than the amount of HCO 3 2 in the total extracellular space. This implies a need for efficient absorptive mechanisms across forestomach epithelia to allow for an early recycling. While Na 1 is absorbed from all forestomachs via Na 1 /H 1 exchange and a non-selective cation channel that shows increased conductance at low concentrations of Mg 21 , Ca 21 or H 1 in the luminal microclima and at low intracellular Mg 21 , HCO 3 2 is secreted by the rumen for the buffering of ingesta but absorbed by the omasum to prevent liberation of CO 2 in the abomasum. Fermentation provides short chain fatty acids and ammonia (NH 3 ) that have to be absorbed both to meet nutrient requirements and maintain ruminal homeostasis of pH and osmolarity. The rumen is an important location for the absorption of essential minerals such as Mg 21 from the diet. Other ions can be absorbed, if delivered in sufficient amounts (Ca 21 , P i , K 1 , Cl 2 and NH 4 1 ). Although the presence of transport mechanisms for these electrolytes has been described earlier, our knowledge about their nature, regulation and crosstalk has increased greatly in the last years. New transport pathways have recently been added to our picture of epithelial transport across rumen and omasum, including an apical non-selective cation conductance, a basolateral anion conductance, an apical H 1 -ATPase, differently expressed anion exchangers and monocarboxylate transporters.Keywords: ruminants, sodium potassium magnesium and calcium, short chain fatty acids, chloride and bicarbonate, channels transporters and exchangers ImplicationsThe improved knowledge of ruminal ion transport clearly underlines its physiological meaning for the whole animal. For example, magnesium absorption is markedly reduced at low Mg and high K intake and the effect of potassium is diminished at high Mg intake. This variable interaction has been quantified recently permitting the prediction of Mg absorption. Great progress has also been made in understanding the interactions between the absorptive pathways for Na, short chain fatty acids and ammonium. The new findings on structure and regulation of various ion transporters will allow a better understanding of the challenges that different diets pose to the maintenance of homeostatic conditions within the rumen and within the cells of the surrounding epithelium, with the implications for the investigation of ruminal adaptation to different diets. Future studies on transport pathways should include the barrier function of rumen epithelium and its possible impairment under harsh feeding conditions.

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“…Thus, chloride entering the rumen with saliva (10-40mmoll -1 ) under in vivo conditions is absorbed into blood against a considerable electrochemical gradient (Sperber and Hyden, 1952;Dobson and Phillipson, 1958;Martens et al, 1991), requiring that the paracellular pathway effectively prevents a reflux.…”

Section: The Barrier Function Of Forestomach Epitheliamentioning

confidence: 99%

Sheep rumen and omasum primary cultures and source epithelia: barrier function aligns with expression of tight junction proteins

Stumpff

Georgi

Mundhenk

et al. 2011

Journal of Experimental Biology

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SUMMARYThe forestomachs of cows and sheep have historically served as important models for the study of epithelial transport. Thus, the ruminal epithelium was among the first tissues in which absorption of chloride against an electrochemical gradient was observed, requiring a tight paracellular barrier to prevent back-leakage. However, little is known about ruminal barrier function, despite the considerable implications for ruminant health. The tight junction proteins of the omasum have never been investigated, and no cell culture model exists. We present a new method for the isolation of cells from forestomach epithelia. Protein expression of cells and source tissues of sheep were studied using western blot, PCR and confocal laser scanning microscopy. Supplementary material available online at

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Mechanism of electrically silent Na and Cl transport across the rumen epithelium of sheep

Cited by 47 publications

References 34 publications

Anion-dependent Mg²⁺influx and a role for a vacuolar H⁺-ATPase in sheep ruminal epithelial cells

Anion-dependent Mg²⁺influx and a role for a vacuolar H⁺-ATPase in sheep ruminal epithelial cells

Transport of cations and anions across forestomach epithelia: conclusions from in vitro studies

Sheep rumen and omasum primary cultures and source epithelia: barrier function aligns with expression of tight junction proteins

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Mechanism of electrically silent Na and Cl transport across the rumen epithelium of sheep

Cited by 47 publications

References 34 publications

Anion-dependent Mg2+influx and a role for a vacuolar H+-ATPase in sheep ruminal epithelial cells

Anion-dependent Mg2+influx and a role for a vacuolar H+-ATPase in sheep ruminal epithelial cells

Transport of cations and anions across forestomach epithelia: conclusions from in vitro studies

Sheep rumen and omasum primary cultures and source epithelia: barrier function aligns with expression of tight junction proteins

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Anion-dependent Mg²⁺influx and a role for a vacuolar H⁺-ATPase in sheep ruminal epithelial cells

Anion-dependent Mg²⁺influx and a role for a vacuolar H⁺-ATPase in sheep ruminal epithelial cells