IN THE CELL. IN VITRO. AND IN RECONSTITUTED MEMBRANES

The hepatocyte of mammalian liver is a highly differentiated polarized cell. The plasma membrane of the hepatocyte is also complex consisting of the following differentiated regions or domains: the perisinusoidal domain facing the liver sinusoid which is carrying blood from the gastrointestinal syste~ of the animal via the hepatic portal vein; lateral domains between two adjacent hepatocytes; the bile canaliculus formed by the opposed mem­ branes of two adjacent hepatocytes; desmosomes. tight and gap junctions; and the basal domain attaching the hepatocyte to its connective tissue sub­ stratum (Figure 1). Each of these domains is comprised of different sets of proteins and possibly lipids which endow the domain with its characteristic function and in some cases a recognizably characteristic morphology at the electron microscope level. The perisinusoidal domain is involved in secre­ tion of serum proteins and the uptake of small and large molecular weight material from the blood. This domain would rontain receptors involved in • •