AJP - Endocrinology and Metabolism, Vol 240, Issue 2 203-E208, Copyright © 1981 by American Physiological Society
Effects of clofibric acid on amino acid metabolism in cultured rat skeletal muscle
W. M. Pardridge, L. Duducgian-Vartavarian, D. Casanello-Ertl, M. R. Jones and J. D. Kopple
Well-differentiated cultured skeletal muscle cells (myotubes) obtained from
adult rats were incubated for up to 48 h in Dulbecco's modified Eagle's
medium. Medium glucose decreased from 4.9 +/- 0.1 mM at 0 h to 13 +/- 1
microM by 24 h; approximately 60% of glucose was converted to lactate.
Pyruvate, alanine, and citrate were continuously produced, even during the
period of 24-48 h when no glucose or lactate utilization was observed.
Branched-chain amino acid utilization increased more than fourfold during
the incubation period of 24-48 h; during this time, intracellular ATP,
pyruvate, alpha-ketoglutarate, malate, and citrate levels were constant
despite the absence of glucose or lactate consumption. Incubation of muscle
cells with 2 mM clofibric acid resulted in a 76% inhibition of leucine
metabolism. Coincident with the drug-induced inhibition of a branched-chain
amino acid utilization, alanine and citrate production was blocked, and
cell levels of pyruvate, alpha-ketoglutarate, malate, and citrate were
markedly reduced. These studies suggest branched-chain amino acids
contribute significantly to anaplerotic pathways in cultured skeletal
muscle cells and that these pathways lead to the net production of alanine
and citrate during periods of minimal carbohydrate utilization.
