ABSENCE OF VACUOLAR H-ATPASES FROM RAT SMALL-INTESTINE BRUSH-BORDER MEMBRANES()

Rat small intestinal brush-border membrane (BBM) vesicles were solubil ized to test for the presence of an intravesicular H+-ATPase. Several detergents that in rat renal BBM vesicles revealed a bafilomycin-sensi tive H+-ATPase failed to expose a similar ATPase in small intestinal v esicles. Antibodies against the 31-kDa and 70-kDa H+-ATPase subunits l abelled respective antigens in the BBM of renal proximal tubules, but not in the BBM of enterocytes. The results demonstrate that a bafilomy cin-sensitive, vacuolar-type H+-ATPase is absent from the BBM of enter ocytes and, hence, cannot contribute to H+ secretion.