FIGURE 14 This drawing summarizes our present interpretations
of VLDL secretion by hepatocytes. It is
suggested that the nascent particle originates within
cisternae of the smooth ER, after synthesis by enzymes in
these membranes ( 16, 47). The lipid particle subsequently
moves to the smooth surfaced ends of rough ER cisternae
either through tubules connecting the smooth and rough
ER or by brief fusion of the two compartments. At this
junction between smooth and rough ER (9, 27), B
apoprotein and probably other VLDL apoproteins are
bound to the lipid particle to form a nascent lipoprotein.
The nascent VLDL are then transported within a tubular
membrane compartment to the Golgi apparatus and are
collected in secretory vesicles developing from this
organelle (9, 22). After concentration and glycosylation
(56), these vesicles transport nascent VLDL to the cell
surface where release into the space of Disse results from
membrane fusion between secretory vesicles and the
plasma membrane