Transport of sodium across the isolated bovine rumen epithelium: interaction with short‐chain fatty acids, chloride and bicarbonate

Sehested, Jakob; Diernæs, L; Møller, Per; Skadhauge, Erik

doi:10.1113/expphysiol.1996.sp003920

Cited by 48 publications

(64 citation statements)

References 15 publications

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“…Chien & Stevens (1972) suggested that ruminal sodium and chloride transport are indirectly coupled due to the parallel existence of a Na¤-H¤ and Cl¦-HCO×¦ exchange. This hypothesis was confirmed in further studies by Martens & G abel (1988) and by Sehested et al (1996). The present study therefore was also designed to elucidate whether cAMP affects chloride transport.…”

supporting

confidence: 60%

Regulatory Role of cAMP in Transport of Na⁺, Cl⁻ and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium

Gäbel

Butter

Martens

1999

Experimental Physiology

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summary Sodium is absorbed in considerable amounts across the ruminal epithelium, whilst its transport is strongly interrelated with the permeation of chloride and short-chain fatty acids (SCFAs). However, regulation of ruminal Na¤, Cl¦, and SCFA absorption is hardly understood. The present study was therefore performed to characterize the influence of cAMP on sodium and sodiumcoupled transport mechanisms in short-circuited, stripped ruminal epithelia of sheep. Elevation of intracellular cAMP concentrations by theophylline (10 mÒ) or theophylline in combination with forskolin (0·1 mÒ) significantly reduced mucosal-to-serosal sodium transport, leading to a reduction of net transport. The theophylline-or theophylline-forskolin-induced reduction of sodium transport was accompanied by a decrease in chloride net transport but revealed no effect on propionate flux. Short-chain fatty acids stimulated Na¤ transport but their stimulatory effect was almost completely blocked by theophylline-forskolin. In solutions with and without SCFAs, the inhibitory effect of 1 mÒ amiloride on sodium transport was strongly reduced after theophylline-forskolin pretreatment of the tissues. Blocking the production of endogenous prostaglandins by addition of indomethacin (10 ìÒ) led to a theophylline-sensitive stimulation of unidirectional and net fluxes of sodium. The findings indicate that apical, amiloride-sensitive Na¤-H¤ exchange andÏor basolateral Na¤-K¤-ATPase can effectively be blocked by cAMP, leading to a decrease in sodium and chloride transport. In the ruminal epithelium, cAMP is a second messenger of prostaglandins, which are released spontaneously under in vitro conditions. introduction Due to the high secretion rate of the salivary glands, the amount of sodium entering the rumen of sheep and cows is 20-40 times greater than the salivary sodium load in monogastric species (Kay, 1960; Bailey, 1961a,b). The ruminal epithelium, in turn, plays an important role in maintaining the sodium balance of the animal since it is able to absorb up to 50% of the sodium secreted by the salivary glands (Dobson, 1959). However, the amount of sodium transported across the ruminal epithelium varies remarkably. An energy rich diet leads to an increase in sodium absorption, whereas food deprivation is accompanied by a sharp decrease (Gaebel et al. 1987;G abel et al. 1993). This adaptive nature of sodium transport suggests the existence of precisely controlled ion transport processes both at the systemic, hormonal level and at the cellular level.As regards control at the cellular level, studies by Wolffram et al. (1989) indicated an influence of cAMP on the transfer of sodium across the ruminal epithelium without, however, elucidating the underlying transport mechanisms. Since apical Na¤-H¤ exchange has been demonstrated to mediate a great part of ruminal sodium transport

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supporting

confidence: 60%

Regulatory Role of cAMP in Transport of Na⁺, Cl⁻ and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium

Gäbel

Butter

Martens

1999

Experimental Physiology

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“…The initial G t and I sc values of the rumen preparations were consistent with previous studies (Sehested et al, 1996a, Aschenbach et al, 2000, Penner et al, 2010 and are representative of viable preparations. The EXT used in these experiments has previously been evaluated in vitro to determine if other compounds are present that could contribute to the observed effects of the EXT (Foote et al, 2012).…”

Section: Resultssupporting

confidence: 75%

“…the buffer contained HCO 3 − and did not contain Cl − or NO 3 − ) and bicarbonate-independent nitrate insensitive VFA flux (passive) by inducing maximal inhibition (i.e. addition of Cl − and NO 3 − and absence of HCO 3 − ) (Sehested et al, 1996a, Penner et al, 2009. Facilitated VFA flux was calculated as the difference between total and passive flux.…”

Section: Methodsmentioning

confidence: 99%

Acute exposure to ergot alkaloids from endophyte-infected tall fescue does not alter absorptive or barrier function of the isolated bovine ruminal epithelium

Foote

Penner

Walpole

et al. 2014

animal

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Ergot alkaloids in endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) have been shown to cause a reduction in blood flow to the rumen epithelium as well as a decrease in volatile fatty acids (VFA) absorption from the washed rumen of steers. Previous data also indicates that incubating an extract of endophyte-infected tall fescue seed causes an increase in the amount of VFA absorbed per unit of blood flow, which could result from an alteration in the absorptive or barrier function of the rumen epithelium. An experiment was conducted to determine the acute effects of an endophyte-infected tall fescue seed extract (EXT) on total, passive or facilitated acetate and butyrate flux across the isolated bovine rumen as well as the barrier function measured by inulin flux and tissue conductance (G t ). Flux of ergovaline across the rumen epithelium was also evaluated. Rumen tissue from the caudal dorsal sac of Holstein steers ( n = 6), fed a common diet, was collected and isolated shortly after slaughter and mounted between two halves of Ussing chambers. In vitro treatments included vehicle control (80% methanol, 0.5% of total volume), Low EXT (50 ng ergovaline/ml) and High EXT (250 ng ergovaline/ml). Results indicate that there is no effect of acute exposure to ergot alkaloids on total, passive or facilitated flux of acetate or butyrate across the isolate bovine rumen epithelium ( P > 0.51). Inulin flux ( P = 0.16) and G t ( P > 0.17) were not affected by EXT treatment, indicating no alteration in barrier function due to acute ergot alkaloid exposure. Ergovaline was detected in the serosal buffer of the High EXT treatment indicating that the flux rate is~0.25 to 0.44 ng/cm 2 per hour. Data indicate that specific pathways for VFA absorption and barrier function of the rumen epithelium are not affected by acute exposure to ergot alkaloids from tall fescue at the concentrations tested. Ergovaline has the potential to be absorbed from the rumen of cattle that could contribute to reduced blood flow and motility and lead to reduced growth rates of cattle.Keywords: bovine, ergovaline absorption, fescue toxicosis, volatile fatty acid absorption ImplicationsResults from this experiment show that ergot alkaloids present in endophyte-infected tall fescue do not have an impact on nutrient absorption or barrier function of the isolated rumen epithelium of cattle following acute exposure. This indicates that previously observed reductions in nutrient absorption in live animals exposed to ergot alkaloids requires chronic exposure or is driven by the reduced blood flow. Results also show that ergovaline, one of the main causative agents of fescue toxicosis, is absorbed across the rumen epithelium, although it is at a fairly slow rate ∼1% of a daily dose.

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“…This context was used repeatedly to explain the stimulatory effects of Cl 2 on the electroneutral absorption of Na 1 , Mg 21 and Ca 21 across rumen epithelium Leonhard et al, 1991;Sehested et al, 1996;Leonhard-Marek et al, 2007a). Additional effects of Cl 2 on electrogenic cation absorption raised the hypothesis that apical Cl 2 channels might mediate a Cl 2 dependent change in membrane potential and thereby increase the electric driving force for cation uptake (Leonhard-Marek and Schrö der, 2002;Leonhard-Marek et al, 2006).…”

Section: Absorption and Secretion Of Chloridementioning

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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Transport of sodium across the isolated bovine rumen epithelium: interaction with short‐chain fatty acids, chloride and bicarbonate

Cited by 48 publications

References 15 publications

Regulatory Role of cAMP in Transport of Na⁺, Cl⁻ and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium

Regulatory Role of cAMP in Transport of Na⁺, Cl⁻ and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium

Acute exposure to ergot alkaloids from endophyte-infected tall fescue does not alter absorptive or barrier function of the isolated bovine ruminal epithelium

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

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Transport of sodium across the isolated bovine rumen epithelium: interaction with short‐chain fatty acids, chloride and bicarbonate

Cited by 48 publications

References 15 publications

Regulatory Role of cAMP in Transport of Na+, Cl− and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium

Regulatory Role of cAMP in Transport of Na+, Cl− and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium

Acute exposure to ergot alkaloids from endophyte-infected tall fescue does not alter absorptive or barrier function of the isolated bovine ruminal epithelium

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

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Regulatory Role of cAMP in Transport of Na⁺, Cl⁻ and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium

Regulatory Role of cAMP in Transport of Na⁺, Cl⁻ and Short‐Chain Fatty Acids Across Sheep Ruminal Epithelium