Distribution of bile acid absorption and bile acid transporter gene message in the hamster ileum

The apical, Na-dependent, ileal bile acid transporter (IBAT) is critical fo r the reabsorption of bile acids in the ileum. Bile acid transport capaciti es as well as the distribution of bile acid transporter messenger ribonucle ic acid (mRNA) and transporter protein were studied along the axis of the i leum. Na-dependent and Na-independent taurocholate uptake was measured in t he hamster ileum using an everted-sleeve technique. The distribution of IBA T mRNA and protein were mapped by in-situ hybridization, immunohistochemist ry, and Western blotting. Na-dependent and Na-independent bile acid uptake rates were highest 1-4 cm before the ileocecal valve (maxima 780 and 120 pm ol/mm(2) per min, respectively) and decreased proximally and distally. Na-i ndependent absorption was increased in the last 6 cm of the ileum. IBAT mRN A and protein expression were linked closely to the distribution of uptake capacity. IBAT mRNA was more abundant near the crypt-villus junction wherea s the protein was expressed evenly along the villus axis. We conclude that Na-dependent and Na-independent bile acid absorption capacities both have d istinct distribution curves in the hamster ileum. All ileocytes on villi in the high-uptake area of the ileum express IBAT mRNA and protein.