The effect of low mucosal pH on sodium and chloride movement across the isolated rumen mucosa of sheep.

Isolated sheets of sheep rumen mucosa were studied in vitro by using the Ussing chamber technique. The pH of the mucosal solution was altered by adding HCl. Using 22Na and 36Cl unidirectional fluxes of sodium and chloride were measured across the short-circuited and voltage-clamped rumen mucosa at mucosal pH 7.4 and 5.5. Lowering mucosal pH to 5.5 caused a rapid decline in the short-circuit current (Isc). The conductance (Gt) increased about 10 min after the drop in Isc. At pH 5.5, mucosal-to-serosal movement of Na+ and Cl- was decreased thus leading to a decreased net transport. These alterations were seen 30 min after mucosal acidification. They were intensified 120 min thereafter. Further studies showed that a clamped transmural potential difference (20 mV) influenced Na+ and Cl- transport only slightly more in acidified epithelia. Light and electron microscopy showed a swelling of the cells and especially of their mitochondria after acid exposure. These data indicate that lowering mucosal pH causes alterations in transepithelial Na+ and Cl- transport. We suggest a predominant effect on cellular transport mechanisms.