Modulation of vH-ATPase is part of the functional adaptation of sheep rumen epithelium to high-energy diet

Ruminal vacuolar H-ATPase (vH-ATPase) activity is regulated by metabolic signals. Thus, we tested whether its localization, expres-sion, and activity were changed by different feeding. Young male sheep (n 12) were either fed hay ad libitum (h) or hay ad libitum plus additional concentrate (h/c) for 2 wk. The vH-ATPase B subunit signal was predominantly found in the cell membrane and cytosol of rumen epithelial cells (REC) with basal/parabasal pheno-type. The elevated number (threefold) of these cells in rumen mucosa of h/c-fed sheep reflects a high proliferative capacity and, explains the 2.3-fold increase of the total number of vH-ATPase-expressing REC. However, in accordance with a 58 % reduction of the vH-ATPase B subunit mRNA expression in h/c-fed sheep, its protein amount per single REC was decreased. Using the fluorescent probe BCECF and selective inhibitors (foliomycin, amiloride), the contri-bution of vH-ATPase and Na/H exchanger to intracellular p