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Department of Kinesiology, University of Southern California, Los Angeles, California 90089
To
determine whether changes in long-chain fatty acid (LCFA) oxidative
metabolism induced by elevated intracellular carbohydrate availability
are due to changes in LCFA uptake or in mitochondrial transport
capacity, rat hindquarters were perfused with 500 µM palmitate and
[1-14C]palmitate or [1-14C]octanoate as
well as with either low (LG) or high (HG) carbohydrate availability.
Glucose uptake was higher in the HG vs. LG group (23.6 ± 1.5 vs
4.7 ± 0.9 µmol · g
1 · h1,
P < 0.05). Palmitate delivery was not significantly
different between groups and averaged 97.1 ± 4.6 nmol · min1 · g1
(P > 0.05). Fractional and total palmitate uptake
values were 60% higher (P < 0.05) in the HG
(0.125 ± 0.012 and 7.4 ± 1.2 nmol · min1 · g1) vs. LG
(0.079 ± 0.009 and 11.8 ± 1.5 nmol · min1 · g1) group.
Values of percent and total palmitate oxidized were significantly lower
(P < 0.05) in the HG (9.1 ± 1.1% and 1.31 ± 0.16 nmol · min1 · g1)
vs. LG (23.4 ± 5.2% and 0.76 ± 0.08 nmol · min1 · g1) group.
Conversely, values of fractional uptake and percent oxidation of
octanoate were not significantly different between groups
(P > 0.05). Malonyl-CoA levels were inversely
correlated with LCFA oxidation (P < 0.05). These
results demonstrate that high carbohydrate availability in muscle is
associated with a decrease in LCFA oxidation that is not due to a
parallel decrease in LCFA uptake; rather, the decrease in LCFA
oxidation could be due to malonyl-CoA inhibition of mitochondrial LCFA transport.
long-chain fatty acid; medium-chain fatty acid; malonyl-coenzyme A; carbohydrate; free fatty acid metabolism; free fatty acid oxidation; free fatty acid uptake
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