Tricarboxylic acid cycle intermediates in human muscle at rest and
during prolonged cycling.
Gibala, Martin J., Mark A. Tarnopolsky, and Terry E. Graham.
Department of Human Biology and Nutritional Sciences, University of
Guelph, Guelph, Ontario, N1G 2W1, CANADA, and Departments of
Kinesiology and Physical Medicine and Rehabilitation, McMaster
University, Hamilton, Ontario, L8S 4K1, CANADA
APStracts 3:0223E, 1996.
Previous studies have used the muscle concentration of (citrate +
malate + fumarate) to estimate tricarboxylic acid (TCA) cycle pool
size in humans [e.g., Am. J. Physiol. 259:C834-C841, 1990]. Our
purpose was to quantify changes in individual TCA cycle intermediates
(TCAI) and total pool size by measuring the concentrations of the 8
TCAI in human muscle. Eight males cycled to exhaustion (Exh) at 70%
of their maximal oxygen uptake and biopsies were obtained from vastus
lateralis at rest and during exercise. Succinyl CoA was not
consistently detectable, but the sum of the other 7 TCAI was 1.23+/
-0.04 at rest, 4.80+/-0.25 and 4.87+/-0.30 after 5 and 15 min of
exercise, respectively, and 3.08+/-0.15 mmol x kg-1 dry weight at
Exh. Pool size during exercise was 50% higher than seen in rodent
muscle following intense electrical stimulation (Eur. J. Biochem.
110:371-377, 1980). Relative changes in individual TCAI were not
uniform, and none was "representative" of the changes in
total pool size. We conclude that changes in specific intermediates
or total pool size cannot be used as indicators cycle flux, and that
the apparent species differences in total pool size may reflect
differences in fibre type composition, recruitment pattern or
relative intensity of contraction.
Received 28 June 1996; accepted in final form 25 October 1996.
APS Manuscript Number E306-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996