Ruminal SCFA absorption: channelling acids without harm

G. Gäbel; J.R. Aschenbach

Ruminal SCFA absorption: channelling acids without harm

In: Ruminant physiology

Authors:

G. Gäbel

G. Gäbel Institute of Veterinary Physiology, Leipzig University, An den Tierkliniken 7, D-04103 Leipzig, Germany

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J.R. Aschenbach

J.R. Aschenbach Institute of Veterinary Physiology, Leipzig University, An den Tierkliniken 7, D-04103 Leipzig, Germany

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Type:: Chapter

Pages:: 173–195

DOI:: https://doi.org/10.3920/9789086865666_007

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Several studies indicate that the bulk absorption of short chain fatty acids (SCFA) occurs in the protonated forms (HSCFA). However, there are strong hints that SCFA are also taken up in their dissociated forms (SCFA-) by anion exchange systems in the apical membrane. On a molecular basis, various transport proteins (anion exchange / AE; putative anion transport / PAT; down-regulated in adenoma / DRA) are characterized which may accept SCFA in their dissociated form. After luminal uptake, SCFA can either be catabolized or extruded on the basolateral (blood-oriented side) of the cell. Intracellular catabolism leads to ketonic acids (acetoacetate, D-3-hydroxybutyrate) and lactate. These monocarboxylates are rather hydrophilic and need specific transport proteins. Recent functional, structural and immunocytochemical studies revealed a monocarboxylate transporter isoform 1 (MCT1) in the stratum basale, which most likely mediates the effective elimination of the ketonic acids and lactic acid into the direction of blood.

Both uptake of HSCFA and exchange of intracellular HCO₃^- for extracellular SCFA- acidify the cytosol. The rumen epithelium has developed sophisticated strategies to eliminate the surplus of protons. The main proton exporting mechanisms seem to be a sodium / proton exchanger isoform 1 (NHE1) and the MCT1 on the basolateral side of the epithelium. Proton extrusion is supported by import of HCO₃^- via a sodium bicarbonate cotransporter isoform 1 (NBC1).

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Ruminant physiology

Digestion, metabolism and impact of nutrition on gene expression, immunology and stress

E-Book ISBN:: 9789086865666

Publisher:: Wageningen Academic

Print Publication Date:: 24 Oct 2006

Subjects
- Life Sciences
  - General
  - Animal & Veterinary

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Ruminal SCFA absorption: channelling acids without harm

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Ruminant physiology

Digestion, metabolism and impact of nutrition on gene expression, immunology and stress

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