Comparison of two bioassays to determine the metabolisable energy of different wheat cultivar samples

1. Occurrence of short chain fatty acids (SCFA) in anionic form limits their diffusion across the absorptive membrane. The present study sought to establish the mechanism of SCFA absorption in the ostrich. 2. Epithelial tissues were taken from the sacculated part of the colon and mounted in Ussing chambers in a bathing solution. The tissues were voltage-clamped and allowed to equilibrate to obtain a baseline short circuit current (Isc). 3. Propionate (23 mm) on the mucosal side increased the Isc. The SCFA-induced Isc was completely inhibited by anoxia, ouabain (1 to 2 mm), acetazolamide (0·5 mm) and 4,4ʹ-diisothiocyanostilbene-2,2ʹ-disulfonic acid (0·1 mm) on the mucosal side. 4. These findings indicate that SCFA stimulate hydrogen ion secretion through an electrogenic H+-K+-ATPase, the source of hydrogen ions being carbonic anhydrase catalysed hydration of CO2. 5. Simultaneous activation of exchange prevents intracellular accumulation of bicarbonate ions. This system may provide hydrogen ions for protonation of SCFA anions and subsequent absorption by non-ionic diffusion.