Participation of NH4+ in total ammonia absorption across the rumen epithelium of sheep (Ovis aries)

1. Participation of NH4+ in total ammonia transport across sheep rumen wall was studied in vitro. 2. In Ussing-type chambers addition of NH4+ or K+ to the incubation solution on the mucosal side of the epithelium evoked positive short circuit currents (I-SC) 3. The K+ induced Ise but not the NH4+ induced I-SC could be blocked by Ba2+ whereas both, K+ or NH4+ induced I-SC were blocked by quinidine. 4. Transepithelial fluxes of ammonia were significantly reduced when quinidine was present in the incubation solution. 5. When the transepithelial potential difference was clamped to -25 mV (polarity on the serosal side) ammonia fluxes from the mucosal to the serosal side were significantly larger than fluxes of ammonia measured at a potential difference of +25 mV. 6. It is suggested that NH4+ takes part in ammonia transport across the rumen epithelium, most probably by using a K+-transport system.