Permeation of acetate across sheep ruminal epithelium is partly mediated by an anion channel

The present study pursued the question if an anion channel could be partly responsible for the transport of acetate in the isolated ovine ruminal epithelium. Using the Ussing chamber technique, changes of short-circuit current (I_sc) induced by mucosal or serosal addition of acetate was investigated. To further evaluate the I_sc changes induced by acetate the epithelia were preincubated with ouabain or 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS). In addition, unidirectional flux rates of ¹⁴C-acetate were measured at different transepithelial potential difference (V_t). At V_t=0mV, acetate addition to the mucosal side of epithelia incubated in ouabain/DIDS free solution resulted in an I_sc decrease, whereas application to the serosal side induced an I_sc increase. Absolute I_sc changes were significantly larger after serosal than after mucosal acetate addition. Ouabain pre-incubation abolished these side-specific differences. Pre-incubation with DIDS on the mucosal side inhibited the current induced by subsequent mucosal acetate addition in a voltage dependent manner, whereas serosal DIDS pre-incubation had no effect on acetate-induced changes of I_sc. Mucosal-to-serosal acetate flux was partly voltage-dependent. The serosal-to-mucosal flux of acetate was not influenced by V_t. The asymmetric changes of I_sc after acetate application and the V_t dependence of the DIDS inhibition on the mucosal side indicate a partly electrogenic transcellular permeation of acetate which includes an apically located acetate conductance. It is suggested that this conductance may be important for epithelial cell homeostasis.