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Cholangiocytes are the epithelial cells of the bile duct. They are cuboidal epithelium in the small interlobular bile ducts, but become columnar and mucus secreting in larger bile ducts approaching the porta hepatis and the extrahepatic ducts.
In the healthy liver, cholangiocytes contribute to bile secretion via net release of bicarbonate and water. Several hormones and locally acting mediators are known to contribute to cholangiocyte fluid/electrolyte secretion. These include secretin, acetylcholine, ATP, and bombesin.
Cholangiocytes act through bile-acid independent bile flow, which is driven by the active transport of electrolytes. In contrast, hepatocytes secrete bile through bile-acid dependent bile flow, which is coupled to canalicular secretion of bile acids via ATP-driven transporters. This results in passive transcellular and paracellular secretion of fluid and electrolytes through an osmotic effect.
Importantly, cholangiocytes are the target of disease in a variety of conditions often known as "cholangiopathies". These diseases include primary biliary cirrhosis, primary sclerosing cholangitis, AIDS cholangiopathy, disappearing bile duct syndromes, Alagille's syndrome, cystic fibrosis, and biliary atresia. As a group, cholangiopathies account for approximately 18% of adult liver transplantations and the majority of pediatric liver transplantations.
Active scientific investigation of cholangiocytes focuses on such diverse processes as mechanisms of fluid/electrolyte secretion, regulation of cholangiocyte proliferation, roles of cholangiocytes in the pathogenesis of liver fibrosis and cirrhosis, and cholangiocyte apoptosis. Specific investigation of individual cholangiopathies is also pursued actively.