Ruminants cover large amounts of their energy requirement by the production and absorption of SCFA in the rumen. The aim of this study was to investigate the possible contribution of transport proteins to acetate absorption and to identify potential transport proteins involved. Influx studies using 14C-labelled acetate were performed with stripped ovine ruminal epithelium of sheep. Acetate absorption increased with decreasing mucosal pH. Omitting bicarbonate from the incubation solution reduced apical uptake of acetate at concentrations ranging from 5 - 60 mM acetate (by up to 35%± 8% at 20 mM acetate). In the absence of bicarbonate, 60 mM nitrate inhibited acetate absorption (by up to 57%± 8% at 10 mM acetate). DRA, PAT1, CFTR, ClC2, ClC4 and ClC5 were detected by RT-PCR. In conclusion, acetate- absorption is mediated not only by lipophilic diffusion but also by specific transport proteins. Candidates for bicarbonate-dependent acetate absorption are DRA and PAT1. Bicarbonate-independent transport might occur via anion channel(s) represented by ClC2, ClC4, ClC 5 and/or CFTR.

The study was supported by the DFG (GA 329/ 5-2 and 6-1) Current address: S Bilk, Physiologisches Institut, Tierärztliche Hochschule Hannover