21 research outputs found
Evidence for NHE3-mediated Na transport in sheep and bovine forestomach
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,
pHi. 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, pHi and volume
regulation