Journal of Lipid Research, Vol 21, 671-680, Copyright © 1980 by Lipid Research, Inc.
Lipoprotein secretion by isolated rat hepatocytes: characterization of the lipid-carrying particles and modulation of their release
HJ Kempen
Lipoprotein production by freshly isolated rat hepatocytes in suspension
was studied during short (1--3 hr) incubation periods. The hepatocytes
release very low density (d < 1.01 g/ml) lipoprotein (VLDL) particles,
which as a group a) contain triaclyglycerols, phospholipids, free
cholesterol, and cholesteryl esters in molar proportions of 100:21:8:4; b)
have a mean diameter 1.5-fold larger than those of plasma VLDL; c) have a
similar electrophoretic mobility as plasma VLDL; and d) carry apoproteins B
and E as major, and apoproteins AI and C as minor, protein components.
These apoproteins in the secreted VLDL can be newly synthesized during the
incubation, as indicated by the incorporation of [14C]leucine. The
secretion of VLDL by the hepatocytes is inhibited by addition of glucagon
or dibutyryl cyclic AMP, and stimulated by added palmitate; thus, as in the
whole liver, the secretory process is under hormonal or substrate control
also in the isolated cells condition. Phospholipids and free cholesterol
are also released as components of particles with higher densities, ranging
from 1.03--1.08 g/ml, and from 1.10 to 1.24 g/ml. Colchicine and
cycloheximide, while strongly suppressing VLDL secretion, inhibit the
release of these other particles to a lesser extent (d 1.03--1.08 g/ml) or
not at all (d > 1.10 g/ml). These particles with higher densities have
not been positively identified; the latter group is dissimilar to the high
density lipoprotein, which occurs in rat liver perfusates, or to rat bile
micelles.
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