kanalikuljetusmanöövereitä

Kanalikuljetus, also known as canalicular transport, is the transcellular movement of substances from the hepatocyte’s apical or canalicular membrane into the bile canaliculi, the tiny channels between adjacent liver cells that drain into the biliary tree. This process is a core component of bile formation, helping to excrete bile acids, phospholipids, cholesterol, bilirubin conjugates, and other solutes into the forming bile.

The canalicular membrane contains several transport proteins that drive this secretion. The bile salt export pump (BSEP, encoded by ABCB11) exports bile acids into the canaliculi, providing the principal osmotic and detergent force for bile formation. MDR3 (ABCB4) translocates phospholipids, mainly phosphatidylcholine, into bile, helping to stabilize bile and protect the biliary tract. MRP2 (ABCC2) transports conjugated organic anions such as bilirubin glucuronides and other metabolites. Additional transporters contribute to the excretion of cholesterol, flavonoids, and various drugs. The canalicular secretion is influenced by hormonal signals and cellular polarity, with tight junctions separating the canalicular lumen from the bloodstream.

Clinical relevance arises when canalicular transport is impaired, leading to cholestasis. Genetic defects in canalicular transporters cause familial intrahepatic cholestasis types PFIC1 (ATP8B1), PFIC2 (ABCB11/BSEP deficiency), and PFIC3 (ABCB4/MDR3 deficiency). Drug-induced cholestasis and other hepatobiliary diseases can also reflect disrupted canalicular transport. Diagnosis combines genetic testing, liver function assessment, imaging, and sometimes liver biopsy. Treatment focuses on symptom relief and managing cholestasis, with ongoing research into restoring transporter function and bile flow.