Characterization, cDNA cloning, and functional expression of mouse ileal sodium-dependent bile acid transporter

Mouse ileal sodium dependent bile acid transporter (ISBT) was characterized using isolated enterocytes. Only enterocytes from the most distal portion showed Na+-dependent [H-3]taurocholate uptake, Northern blot analysis using a probe against mouse ISBT revealed the expression of mouse ISBT mRNA to b e restricted to the distal ileum, The K-m and V-max for Na+-dependent [H-3] taurocholate transport into isolated ileocytes were calculated as 27 mu M a nd 360 pmol/mg protein/min, respectively. Uptake of [H-3]taurocholate was i nhibited by N-ethylmaleimide, We have cloned ISBT cDNA from mouse ileum. Th e cDNA included the entire open reading frame coding 348 amino acid protein with seven hydrophobic segments and two N-glycosylation sites. COS-7 cells transfected with the expression vector containing this cDNA expressed Na+- dependent [H-3] taurocholate uptake activity with a K-m of 34 mu M.