J. Biol. Chem., Vol. 265, Issue 13, 7195-7201, May, 1990
Ethanolamine metabolism in cultured bovine aortic endothelial cells
BA Lipton, EP Davidson, BH Ginsberg and MA Yorek
Department of Biochemistry, University of Iowa, Iowa City 52246.
The role of extracellular ethanolamine in phospholipid synthesis was
examined in cultured bovine aortic endothelial cells. Serine and
ethanolamine were both readily accumulated by these cells and incorporated
into phospholipid. Exposing cells to extracellular ethanolamine for 4-6
weeks had no effect on cell growth, yet increased the
phosphatidylethanolamine content of these cells by 31% as compared to
control cells. The intracellular content of ethanolamine was measured by
high performance liquid chromatography, and results showed that the
ethanolamine-treated cells contained a significantly greater amount of free
ethanolamine compared to control cells (0.62 +/- 0.07 nmol/mg of protein
versus 0.27 +/- 0.05 nmol/mg of protein, respectively).
Ethanolamine-treated cells also had decreased accumulation and
incorporation into lipid of [3H]ethanolamine throughout a 48-h incubation
and increased K'm and V'max parameters of ethanolamine transport as
compared to control cells. Studies were also done to examine the effect of
ethanolamine on the generation of free ethanolamine from
phosphatidylserine. In pulse-chase experiments with [3H]serine, a
physiological concentration of ethanolamine (25 microM) decreased the
amount of 3H-labeled phosphatidylethanolamine produced from 3H-labeled
phosphatidylserine by 12 h as compared to the amount of 3H-labeled
phosphatidyl-ethanolamine produced in the absence of ethanolamine in the
chase incubation. Furthermore, ethanolamine-treated cells accumulated 20%
less labeled ethanolamine in the aqueous pool from [3H]serine after 24 h of
incubation than did control cells. These results can be explained by
isotope dilution with the ethanolamine pool that accumulates in these cells
with time when exposed to media supplemented with a physiological
concentration of ethanolamine and by an effect of ethanolamine on
ethanolamine generation from phosphatidylserine. The results show that an
extracellular source of ethanolamine significantly influences the
phospholipid metabolism of cultured bovine aortic endothelial cells.