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    Evidentence for NHE3-mediated Na transport in sheep and bovine forestomach (2011)

    Art
    Zeitschriftenartikel / wissenschaftlicher Beitrag
    Autoren
    Rabbani, I.
    Siegling-Vlitakis, C.
    Noci, B.
    Martens, H.
    Quelle
    Dönerci Dergisi; 301 — S. 313–319
    Sprache
    Englisch
    Verweise
    URL (Volltext): http://ajpregu.physiology.org/content/301/2/R313.full.pdf+html
    Pubmed: 21613579
    Kontakt
    Klinik für Klauentiere

    Königsweg 65
    Gebäude 26
    14163 Berlin
    Tel.+49 30 838 62261 Fax.+49 30 838 62512
    email:klauentierklinik@vetmed.fu-berlin.de

    Abstract / Zusammenfassung

    Na absorption across the cornified, multilayered, and squamous rumen epithelium is mediated by electrogenic amiloride-insensitive transport and by electroneutral Na transport. High concentrations of amiloride (>100 μM) inhibit Na transport, indicating Na(+)/H(+) exchange (NHE) activity. The underlying NHE isoform for transepithelial Na absorption was characterized by mucosal application of the specific inhibitor HOE642 for NHE1 and S3226 for NHE3 in Ussing chamber studies with isolated epithelia from bovine and sheep forestomach. S3226 (1 μM; NHE3 inhibitor) abolished electroneutral Na transport under control conditions and also the short-chain fatty acid-induced increase of Na transport via NHE. However, HOE642 (30 μM; NHE1 inhibitor) did not change Na transport rates. NHE3 was immunohistochemically localized in membranes of the upper layers toward the lumen. Expression of NHE1 and NHE3 has been previously demonstrated by RT-PCR, and earlier experiments with isolated rumen epithelial cells have shown the activity of both NHE1 and NHE3. Obviously, both isoforms are involved in the regulation of intracellular pH, pH(i). However, transepithelial Na transport is only mediated by apical uptake via NHE3 in connection with extrusion of Na by the basolaterally located Na-K-ATPase. The missing involvement of NHE1 in transepithelial Na transport suggests that the proposed "job sharing" in epithelia between these two isoforms probably also applies to forestomach epithelia: NHE3 for transepithelial transport and NHE1 for, among others, pH(i) and volume regulation.