A molecule of extracellular bile salt (glyco- or taurocholate, or glyco- or taurochenodeoxycholate) and two sodium ions are transported into the cytosol, mediated by NTCP (Na+ / taurocholate cotransporter) in the plasma membrane. Bile salts exist in the blood as complexes with serum albumin, and their uptake by NTCP must involve disruption of this complex, but the molecular mechanism of the coupling of the release of a bile salt from albumin to its uptake by NTCP is unknown. In the body, NTCP is expressed on the basolateral surfaces of hepatocytes, and this reaction is the major route by which bile salts reaborbed from the intestinal lumen into the portal circulation are recovered by the liver (Kullak-Ublick et al. 2004; Trauner and Boyer 2002).