membrane contamination and thus could then be used to study transport function when pre- pared as membrane vesicles. These approaches defined a number of transport functions in the plasma membranes of hepatocyres and ultimately led to the recognition that bile salts and 3 25 other solutes were transported into bile largely by ATP dependent transport mechanisms.2 - The advent ofmolecular cloning techniques and cellular expression systems rapidly acceler- ated progress in this field and led to the molecular characterization ofmost ofthe major mem- brane transport proteins that determine both...