ABSTRACT
Bile is made as the result of active transport of its constituents into the biliary
space. Most of this transport occurs across the canalicular membrane, with a further
contribution from cholangiocytes. Water moves passively into bile. The major substrates
that are transported out of hepatocytes are bile acids, phospholipids, cholesterol,
and bilirubin. With the exception of cholesterol, each of these major substrates is
now recognized to have its own transport mechanism. In the case of bile acids and
phospholipids, the transporters appear to be specific, though the bilirubin transporter
is multispecific. Isolated autosomal recessive defects in all three of these transporters
have now been identified and have helped to confirm the physiologic role of these
proteins. In addition, a secondary defect in bile acid transport has been identified
that appears to be due to an abnormality in plasma membrane aminophospholipid distribution.
KEYWORD
progressive familial intrahepatic cholestasis - Dubin-Johnson syndrome - benign recurrent
intrahepatic cholestasis - intrahepatic cholestasis of pregnancy