Taurocholate transport by basolateral plasma membrane vesicles isolated from human liver

Area of Science:

• Hepatology
• Membrane Transport
• Biochemistry

Background:

• Bile acid transport into hepatocytes is crucial for liver function.
• A sodium-dependent, carrier-mediated system transports taurocholate against gradients.
• This system was characterized in rodents but not yet demonstrated in humans.

Purpose of the Study:

• To investigate and demonstrate the presence of the taurocholate cotransporter in human liver.
• To characterize the transport mechanism, including its dependence on sodium and electrical potential.

Main Methods:

• Preparation of basolateral liver plasma membrane vesicles from human liver tissue.
• Enrichment and characterization of membrane fractions using marker enzymes (Na+,K+-ATPase, Mg++-ATPase, alkaline phosphatase).
• Measurement of taurocholate uptake under various ionic gradients and conditions.

Main Results:

• Human liver plasma membrane vesicles were successfully isolated and characterized.
• A sodium gradient energized concentrative taurocholate uptake, exhibiting an overshoot phenomenon.
• The transport mechanism appeared electroneutral and was influenced by the accompanying anion (chloride).
• Uptake was inhibited by other bile acids and bromsulfophthalein.

Conclusions:

• A sodium-dependent, carrier-mediated system for taurocholate transport exists in human hepatocytes.
• This transporter is likely electroneutral and plays a significant role in bile acid uptake.
• The findings provide the first demonstration of this critical transport system in humans.