A molecule of extracellular bile salt or bile acid (cholate, chenodeoxycholate, or their glycine or taurine conjugates) and a sodium ion are transported into the cytosol, mediated by ASBT (apical sodium-dependent bile acid transporter; SLC10A2) in the plasma membrane. In the body, ASBT is expressed on the apical surfaces of enterocytes, and this reaction is the first step in the process by which bile salts and acids are reaborbed from the intestinal lumen and returned to the liver (Kullak-Ublick et al. 2004, Trauner & Boyer 2002). Cytosolic ileal bile acid binding protein (IBABP, FABP6) mediates the transcellular movement of bile acids to the basolateral membrane across which they exit the cells via organic solute transporters (OST) (Kurz et al. 2003).