Journal of Lipid Research, Vol 34, 1873-1881, Copyright © 1993 by Lipid Research, Inc.
Involvement of the lysosome in the catabolism of intracellular lysophosphatidylcholine and evidence for distinct pools of lysophosphatidylcholine
GM Hatch, A Oskin and DE Vance
Lipid and Lipoprotein Research Group, University of Alberta, Edmonton, Canada.
The role of the lysosome in the metabolism of lysophosphatidylcholine was
investigated in isolated rat hepatocytes. Chloroquine, primaquine, and
ammonium chloride caused a 2.5-fold increase in radioactive
lysophosphatidylcholine in [methyl-3H]choline-labeled cells. This effect
was confirmed by a 1.7-fold increase in lysophosphatidylcholine mass in
chloroquine-treated hepatocytes. Chloroquine caused a 2.7-fold increase in
radioactive lysophosphatidylethanolamine in [1- 3H]ethanolamine-labeled
cells and a 2.3-fold increase in radioactive lysophosphatidylcholine in
[methyl-3H]methionine-labeled cells. Chloroquine did not affect formation
of choline-containing aqueous metabolites or the level of radioactivity in
phosphatidylcholine (PC). The effect of chloroquine on radioactive
lysophosphatidylcholine accumulation was concentration-dependent and
occurred within 10 min, consistent with rapid inhibition of lysosomal
function. As there was no observed decrease in the 3H in PC, the
accumulation of lysophosphatidylcholine was likely due to the inhibition of
acid lysophospholipase activity in chloroquine-treated cells. The
accumulation of lysophosphatidylcholine in the presence of chloroquine was
observed in both short-term- (30 min) and equilibrium-(24 h)
[methyl-3H]choline-labeled cells. Simultaneous incubation of hepatocytes
with both albumin and chloroquine increased the radioactivity in
lysophosphatidylcholine in the medium independently of the accumulation of
radioactive lysophosphatidylcholine in the cells. The results suggest that
there are separate pools of lysophosphatidylcholine in the hepatocyte and
that the pool donated to an extracellular acceptor is different from the
lysosomal pool.(ABSTRACT TRUNCATED AT 250 WORDS)
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