Effect of pH on the Transport Capacity of Na+ Across the Isolated Omasal and Ruminal Epithelia of Sheep

Abstract

This study was conducted in attempt to characterize the electroneutral transport of Na⁺ across isolated omasmal and ruminal epithelia of sheep after treatment with pH and amiloride. The conventional Ussing chamber technique was used to measure the mucosal to serosal flux (J_ms), the serosal to mucosal flux (J_sm), the net flux (J_net), the short circuit current (I_sc), and tissue conductance (G_t) of isolated epithelia. A total of 12 pairs of omasmal and ruminal epithelia were used for each treatment, which categorized as: control group (pH 7.4), low pH group (pH 6.4), amiloride group (pH 7.4) and amiloride + low pH group (pH 6.4). The unidirectional transport values of Na⁺ were significantly (p<0.001) higher in the omasum compared to the rumen. Lowering the pH to 6.4 significantly (p<0.001) enhanced the unidirectional transport of Na⁺ in the omasum accompanied by marked changes in the electrochemical parameters (I_sc and G_t); however, the enhancement of the unidirectional flux of Na⁺ in the rumen did not reach the significant level. Application of amiloride in the mucosal side caused a significant (p<0.001) reduction in J_ms, J_sm and J_net of both epithelia. The findings confirmed that Na⁺ transported by means of electroneutral transport systems in the omasum was similar to the system confirmed previously in the rumen. The electroneutral transport of Na⁺ in the omasum is more efficient than the that in the rumen.