Reversible high affinity uptake of apo E-free high density lipoproteins in cultured pig hepatocytes

Journal Article · · Arteriosclerosis (Dallas); (United States)

DOI:https://doi.org/10.1161/01.ATV.5.2.142· OSTI ID:5666200

Bachorik, P S; Franklin, Jr, F A; Virgil, D G; Kwiterovich, Jr, P O

An examination was made of the high affinity binding, uptake, and degradation of apo E-free /sup 125/I-high density lipoprotein (HDL) in cultured pig hepatocytes. At steady state, the cells degraded 9.4% of cell-associated /sup 125/I-HDL/hour, compared with 41.7%/hour for /sup 125/I-LDL. Pulse-chase experiments at 4 degrees C revealed that high affinity /sup 125/I-HDL binding was reversible. Similar experiments at 37 degrees C revealed that about 70% of the cell-associated /sup 125/I-HDL was released as a macromolecule; the remainder was degraded to acid-soluble products. In contrast, over 75% of the /sup 125/I-LDL that was released had been degraded to acid soluble products. The amount of macromolecular /sup 125/I-HDL released at 37 degrees C was similar to the amount that was bound to the cell surface, as estimated from measurements of trypsin-releasable radioactivity. Density gradient ultracentrifugation and SDS-polyacrylamide gel electrophoretic analysis of macromolecular /sup 125/I-HDL released to the medium revealed an increase in density, and the apparent partial proteolysis of apo A-I (Mr 25,000) to products of apparent Mr 12,000-14,000. Measurement of /sup 125/I-HDL and /sup 125/I-LDL degradation in cell homogenates revealed no difference in the inherent susceptibility of the two lipoproteins to proteolysis by lysosomal enzymes. The overall slower rate of degradation of /sup 125/I-HDL compared to /sup 125/I-LDL was therefore due in part to the smaller fraction of HDL that was committed to irreversible catabolism. Cells pulsed at 4 degrees C and subsequently warmed to 37 degrees C released one-half the acid-soluble products from /sup 125/I-HDL within about 4 hours, compared with 2 hours for cells pulsed with /sup 125/I-LDL.

• Research Organization: Johns Hopkins Univ. School of Medicine, Baltimore, MD
• OSTI ID: 5666200
• Journal Information: Arteriosclerosis (Dallas); (United States), Journal Name: Arteriosclerosis (Dallas); (United States) Vol. 5:2; ISSN ARTRD
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AFFINITY
ANIMAL CELLS
ANIMALS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CATABOLISM
CELL CULTURES
CHEMICAL BONDS
DAYS LIVING RADIOISOTOPES
DOMESTIC ANIMALS
ELECTRON CAPTURE RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPES
KINETICS
LIPIDS
LIPOPROTEINS
LIVER CELLS
MAMMALS
METABOLISM
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
PROTEINS
RADIOISOTOPES
REACTION KINETICS
SOMATIC CELLS
SWINE
VERTEBRATES