Zonal distribution of chylomicron remnant uptake in rat liver parenchymal cells

The binding and internalization of chylomicron remnants in rat hepatocytes originating from the periportal and perivenous zones was compared. The hepatocyte sub-populations were separated by centrifugal elutriation and incubated with 125I-labelled chylomicron remnants at 37 degrees C (to measure binding and internalization) or 4 degrees C (to measure initial binding). Periportal and perivenous cells bound and internalised similar amounts of remnants up to a concentration of about 25 micrograms remnant protein per assay, but at higher concentrations the periportal cells were able to internalise significantly more remnants. When excess unlabelled low density lipoprotein was added to the incubations, little effect on the kinetics of either binding or internalization of the remnants was observed. Lactoferrin, an inhibitor of uptake via the remnant receptor, also did not affect the initial binding of the remnants to either cell type, but decreased internalization to similar extents in both sub-populations. These results suggest that periportal hepatocytes have a greater capacity for the uptake of chylomicron remnants than perivenous cells, and that the remnant receptor plays a more important role than the low density lipoprotein receptor in both sub-populations. This acinar heterogeneity parallels that reported previously for cholesterol de novo synthesis, bile formation, lipid content and hepatic lipase secretion.