Regulation of skeletal muscle glycogen phosphorylase and pdh during
maximal intermittent exercise.
Parolin, Michelle L., Alan Chesley, Mark P. Matsos, Lawrence L.
Spriet, Norman L. Jones, and George J. F. Heigenhauser.
1Department of Medicine, McMaster University, Hamilton, Ontario,
L8N 3Z5, Canada, and 2Department of Human Biology and Nutritional
Sciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
APStracts 6:0164E, 1999.
The time course for the activation of glycogen phosphorylase (PHOS)
and pyruvate dehydrogenase (PDH) and their allosteric regulators were
determined in human skeletal muscle during repeated bouts of maximal
exercise. Six subjects completed three 30-s bouts of maximal
isokinetic cycling separated by 4 min recovery periods. Muscle
biopsies were taken at rest, and at 6, 15 and 30s of exercise during
bouts 1 and 3. PHOS was rapidly activated within the first 6s of bout
1 from 12% at rest to 47% at 6s. The activation of PDH increased from
14% at rest to 48% at 6s and 95% at 15s of bout 1. PHOS reverted back
to basal values at the end of the first bout, whereas PDH remained
fully activated. In contrast, in the third bout, PDH was 42% at rest
and was activated more rapidly and was nearly completely activated by
6s, whereas glycogen phosphorylase remained at basal levels (range
14-20%). Lactate accumulation was marked in the first bout and
increased progressively from 2.7 to 76.1 mmol[beta]kg dw-1 with no
further increase in bout 3. Glycogen utilization was also marked in
the first bout and was negligible in bout 3. The rapid activation of
PHOS and slower activation of PDH in bout 1 was probably due to Ca2+
release from the sarcoplasmic reticulum. Lactate accumulation
appeared to be due to an imbalance of the relative activities of PHOS
and PDH. The increase in [H+] may have served to reduce pyruvate
production by inhibiting PHOS transformation and may have
simultaneously activated PDH in the third bout, such that there was a
better matching between pyruvate production and oxidation, and
minimal lactate accumulation. As each bout progressed and with
successive bouts, there was a decreasing ability to stimulate
substrate phosphorylation through PCr hydrolysis and glycolysis and a
shift toward greater reliance on oxidative phosphorylation.
Received 14 December 1998; accepted in final form 23 June 1999.
APS Manuscript Number E561-8.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 9 July 1999