Which transporter mediates uptake of bile acids across the apical membrane in the ileum?

• A. NTCP
• B. Apical sodium-dependent bile acid transporter (ASBT)
• C. OATP
• D. BSEP

Answer: (B)

Uptake of bile acids from the intestinal lumen into enterocytes of the ileum is carried out by a specific apical transporter that uses the sodium gradient. This is the Apical sodium-dependent bile acid transporter, ASBT, which sits on the luminal surface and co-transports bile acids into the cell. It handles both conjugated and unconjugated bile acids as part of enterohepatic circulation. Once inside the enterocyte, bile acids exit basolaterally into portal blood via OSTα/OSTβ, returning to the liver. The other transporters function elsewhere or at different surfaces: NTCP and OATP are hepatic uptake systems, and BSEP exports bile acids into bile from hepatocytes.