Fachbereich Veterinärmedizin


Service-Navigation

    Publikationsdatenbank

    Sizing the pore of the ruminal anion channel (2011)

    Art
    Zeitschriftenartikel / wissenschaftlicher Beitrag
    Autoren
    Stumpff, F.
    Georgi, M.
    Martens, H.
    Aschenbach, J. R.
    Quelle
    Acta physiologica Scandinavica; 201(Suppl. 682) — S. 326–327
    ISSN: 0001-6772
    Sprache
    Englisch
    Kontakt
    Institut für Veterinär-Physiologie

    Oertzenweg 19 b
    14163 Berlin
    Tel.+49 30 838 62600 Fax.+49 30 838-62610
    email:physiologie@vetmed.fu-berlin.de

    Abstract / Zusammenfassung

    Question:
    The rumen has long served as a model tissue for studying the transport of short chain fatty acids. In a recent publication, we suggested that basolateral efflux of acetate may involve a large conductance anion channel. The question arises what other complex organic anions can permeate.

    Methods:
    The patch clamp technique was used to determine the permeability of ruminal epithelial cells to various anions. Estimates for the atomic or molecular dimensions of the anions studied (anhydrated and hydrated) were obtained from the literature.

    Results:
    Whole cell experiments yielded a permeability sequence of p(NO3-) > p(Br-) [asymp] p(I-) [asymp] p(Cl-) > p(HCO3-) > p(acetate-) > p(F-) > p(propionate-) > p(butyrate-) > p(gluconate-). Single channel data showed a conductance of p(Cl) [asymp] 350 pS, p(acetate-) [asymp] 140 pS and p(propionate-) [asymp] 100 pS.

    Conclusions:
    The low permeability for F- indicates that a removal of the hydration shell is necessary to allow passage through the channel pore, suggesting a pore diameter smaller than that of the smallest hydrated anion (Br-[asymp] 6.6 Å). Acetate (width 5.3 Å, length: 6.4 Å) falls below this limit. To allow passage of propionate (5.6 Å x 7.4 Å) and butyrate (5.5 Å x 8.2 Å), the pore diameter has to be larger than 5.6 Å. Passage is apparently delayed by the long tails, which have to be oriented in parallel to the channel axis. The data suggest that the passage of complex anions such as gluconate (width 8.3 Å) or ATP (width 9.7 Å) is unlikely.