Butyrate Permeation across the Isolated Ovine Reticulum Epithelium.

We hypothesized that, due to the high pH of this compartment, the reticulum epithelium displays particular features in the transport of short-chain fatty acids (SCFA). Ovine reticulum epithelium was incubated in Ussing chambers using a bicarbonate-free buffer solution containing butyrate (20 mmol L). p-hydroxymercuribenzoic acid (pHMB), 5-(N-Ethyl-N-isopropyl)amiloride (EIPA), or ouabain were added to the buffer solution as inhibitors of monocarboxylate transporters, sodium-proton-exchangers, or the Na/K-ATPase, respectively. The short-circuit current (I) and transepithelial conductance (G) were monitored continuously while the flux rates of C-labelled butyrate were measured in the mucosal-to-serosal (J) or serosal-to-mucosal direction (J). Under control conditions, the mean values of I and G amounted to 2.54 ± 0.46 µEq cm h and 6.02 ± 3.3 mS cm, respectively. J was 2.1 ± 1.01 µmol cm h on average and about twice as high as J. Incubation with ouabain reduced J, while J was not affected. The serosal addition of EIPA did not affect J but reduced J by about 10%. The addition of pHMB to the mucosal or serosal solution reduced J but had no effect on J. Mucosally applied pHMB provoked a transient increase in the I. The serosal pHMB sharply reduced I. Our results demonstrate that butyrate can be effectively transported across the reticulum epithelium. The mechanisms involved in this absorption differ from those known from the rumen epithelium.