Transport of Na and Cl across the epithelium of ruminant forestomachs: Rumen and omasum. A review

Martens, H.; Gäbel, Gotthold

doi:10.1016/0300-9629(88)90669-x

Cited by 36 publications

(47 citation statements)

References 28 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: 72%

“…According to studies conducted so far, electrogenic pathways in ruminal epithelium are either represented by sodium channels (Martens & G abel, 1988) or by sodium-glucose cotransport proteins (SGLT; Lindemann et al 1996). However, SGLT transporters have generally been shown to be upregulated by cAMP (Debnam, 1994;Wright et al 1997), contradicting the assumption that cAMP-induced decrease in short-circuit current is due to the action of cAMP on SGLT in ruminal epithelium.…”

Section: Discussionmentioning

confidence: 99%

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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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confidence: 72%

Section: Discussionmentioning

confidence: 99%

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 experimental conditions that caused the increase of urea transport in this study (Tables 3, 4, and 6; Fig. 4) are similar to those in corresponding studies in which the stimulatory effect of these fermentation products on amiloride-sensitive Na ϩ absorption via NHE has been characterized (24,26,53,54,77). As in monogastric animals in which Na ϩ uptake also increases in response to a change in the luminal end products of digestion (20), the underlying transporter is NHE3, an extremely well-characterized transport protein that utilizes the energy from the influx of Na ϩ to drive the efflux of H ϩ on a 1:1 basis, in allosterically regulated manner so that the extrusion of protons stops when the cytosolic pH reaches the set point optimal for cellular function (3,20,91).…”

Section: Na and Urea Transportsupporting

confidence: 59%

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO₂

Abdoun

Stumpff

Rabbani

et al. 2010

American Journal of Physiology-Gastrointestinal and Liver Physi

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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 CO2 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 ruminal epithelium of sheep. The flux of urea was found to be phloretin sensitive and passive. At a luminal pH of 6.4, but not at 7.4, the addition of SCFA (40 mmol/l) or CO2/HCO 3 Ϫ (10% and 25 mmol/l) led to a fourfold increase in urea flux. The stepwise reduction of luminal pH in the presence of SCFA from 7.4 to 5.4 led to a bell-shaped modification of urea transport, with a maximum at pH 6.2. Lowering the pH in the absence of SCFA or CO2 had no effect. Inhibition of Na ϩ /H ϩ exchange increased urea flux at pH 7.4, with a decrease being seen at pH 6.4. In experiments with double-barreled, pH-sensitive microelectrodes, we confirmed the presence of an apical pH microclimate and demonstrated the acidifying effects of SCFA on the underlying epithelium. We confirm that the permeability of the ruminal epithelium to urea involves a phloretin-sensitive pathway. We present clear evidence for the regulation of urea transport by strategies that alter intracellular pH, with permeability being highest after a moderate decrease. The well-known postprandial stimulation of urea transport to the rumen in vivo may involve acute pH-dependent effects of intraruminal SCFA and CO2 on the function of existing urea transporters. pH i; urea transporter-B; short-chain fatty acids; microclimate; volatile fatty acid UREA, POSSIBLY BECAUSE OF its small size, was long thought to move passively across epithelia, depending only on the rate of delivery via blood. The urea permeability of cellular membranes has now been established to be several orders of magnitude above that of lipid membranes (11,92) and is coupled to the expression of specific urea-transporting proteins with channel-like kinetics (7,46,71,81,82,95). Whereas the role that these proteins play in the elegant renal concentrating mechanism has received much attention, their function and regulation in other parts of the body, such as the gut (39), continues to be poorly understood.In contrast to the paucity of our knowledge concerning extrarenal urea transport in humans, we have long known of the ability of camels, cows, or sheep to shift the excretion of urea from the kidney (62, 72) to the gastrointestinal tract (79). The transport of urea through the rumen epithelium was first demonstrated many years ago in vivo and in vitro (16,29,79,89) and the physiological significance is clear: in the rumen, dietary cellulose is broken down by bacteria that utilize ureanitrogen for the synthesis of microbial proteins. After passage into the duodenum, the amino acids of these proteins are absorbed and reach the liver, where new urea for secretion into the rumen can be formed. Recycling of nitrogen via urea secretion into the rumen thus ...

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“…Immunohistochemical staining for the a-subunit of this protein was most prominent at the basal membrane of cells within the stratum basale with decreasing staining intensity toward stratum spinosum and granulosum (see also Schnorr, 1971;Graham and Simmons, 2005). Blocking the Na 1 /K 1 -ATPase by the basolateral addition of ouabain abolishes the net Na 1 absorption across reticulum, rumen and omasum (Harrison et al, 1975;Martens and Gä bel, 1988;.…”

Section: Absorption Of Sodiummentioning

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 Na and Cl across the epithelium of ruminant forestomachs: Rumen and omasum. A review

Cited by 36 publications

References 28 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

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO₂

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

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Transport of Na and Cl across the epithelium of ruminant forestomachs: Rumen and omasum. A review

Cited by 36 publications

References 28 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

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO2

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

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO₂