Abstract
A new method to investigate the active excretory process of drugs from the hepatocytes into the bile canaliculi has been developed. This method is, briefly speaking, to retrogradely infuse several reagents through a tubing which is cannulated into the common bile duct and the bile-canalicular membrane of the hepatocytes is thought to be mainly solubilized or modified by infusing surfactants, organic solvents, proteases, lipase, metabolic inhibitors and thiol reagents, because both polyacrylamide gel electrophoretical patterns and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoretical patterns of the bile which was obtained following intrabiliary retrograde infusion of Triton X-100 and SDS display the existance of more proteins than that of normal bile. Moreover, the active excretion of organic anionic dyes, bromphenol blue and uranine, from the hepatocytes into bile was almost inhibited by infusing surfactants retrogradely. The active excretory system is thought to have the following characteristics : it could be solubilized by surfactants and organic solvents, ethanol-ether (3 : 1) and acetone and it is affected by phospholipase D or thiol reagents, p-chloromercuribenzene sulfonic acid and N-ethylmaleimide. A bile-canalicular membrane protein to which the three organic anionic dyes, bromphenol blue, uranine and eosine, are bound has been detected in the Triton X-100 solubilized membrane fraction by polyacrylamide gel electrophoresis and the molecular weight is estimated to be about 80000 by SDS polyacrylamide gel electrophoresis.
