Publikationsdatenbank

The permeability of the large conductance anion channel of the ruminal epithelium decreases with increasing chain length (2010)

Art

Poster

Autoren

Stumpff

Georgi

Martens

Kongress

Joint meeting of the Scandinavian and German Physiological Societies

Copenhagen/Denmark, 27. – 30.03.2010

Quelle

Acta physiologica : official journal of the Federation of European Physiological Societies

Seiten: P – Mon

ISSN: 1748-1716

Sprache

Englisch

Kontakt

Institut für Veterinär-Physiologie

Oertzenweg 19 b
14163 Berlin
+49 30 838 62600
physiologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

Objective: The energy requirements of cows and sheep are met by ruminal fermentation of cellulose into short chain fatty acids (SCFA), which are extensively absorbed by forestomach epithelia. While disappearance rates from the rumen support a permeability sequence of butyrate > propionate > acetate, efflux rates into the blood suggest an inverse order. Basolateral efflux has recently been proposed to occur via a large conductance anion channel. The object of the current study was to characterize this channel in more detail. Methods: Isolated cells of the ruminal epithelium were studied with the patch clamp technique. Results: The permeability of the whole cell membrane for halides showed a loose correlation to the hydration energies, with the permeability for fluoride clearly lower than that for the other halides (P(F)/P(Cl)=0.45 ± 0.04, n = 10; P(Br)/P(Cl)=1.01 ± 0.08, n = 10; P(I)/P(Cl)=1.05 ± 0.08, n = 10). The permeability of the channel for the polyatomic anions tested decreased with molecular size (P(acetate)/P(Cl): 0.42 ± 0.01, n = 16; P(propionate)/P(Cl): 0.39 ± 0.01, n = 47; P(butyrate)/P(Cl): 0.36 ± 0.02, n = 32; P(gluconate)/P(Cl): 0.26 ± 0.01; n = 39), possibly reflecting a decrease in binding energy due to greater partial charge distribution or other steric effects. Single channel measurements confirm the whole cell permeability sequence, with the conductance for propionate (114 ± 10 pS) lower than that previously measured for chloride (350 ± 7 pS) or acetate (142 ± 7 pS). Conclusions: Ruminal epithelial cells express a large conductance anion channel with a moderately weak field strength selectivity site for monoatomic anions. The passage rates of the polyatomic anions of SCFA decrease in the order acetate- > propionate- > butyrate-, reflecting the order of appearance in portal blood. The low passage rate of butyrate- through the channel may explain why this SCFA is so extensively retained and metabolized within the ruminal epithelium.