Glycogen and glycogen phosphorylase associated with sarcoplasmic reticulum:
effects of fatiguing activity.
Lees, Simon J., Peter D. Franks, Espen E. Spangenburg, and Jay H. Williams.
Muscular Function Laboratory, Department of Human Nutrition, Foods, and Exercise,
Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
APStracts 8:0325A, 2001.
The purpose of the present study was to investigate the effects of fatiguing muscular
activity on glycogen, glycogen phosphorylase (GP), and Ca2+ uptake associated with the
sarcoplasmic reticulum (SR). Tetanic contractions (100 ms, 75 Hz) of the gastrocnemius
and plantaris muscles, elicited once per second for 15 min, significantly reduced force to
26.5 ± 4.0% and whole muscle glycogen to 23% of rested levels. SR glycogen levels
were 415.4 ± 76.6 and 20.4 ± 2.1 µg/mg SR protein in rested and fatigued samples,
respectively. The optical density of GP from SDS-PAGE was reduced to 21% of control,
whereas pyridoxal 5«prime»-phosphate concentration, a quantitative indicator of GP
content, was significantly reduced to 3% of control. GP activity after exercise, in the
direction of glycogen breakdown, was reduced to 4% of control. Maximum SR Ca2+
uptake rate was also significantly reduced to 81% of control. These data demonstrate that
glycogen and GP associated with skeletal muscle SR are reduced after fatiguing activity.
Received 3 January 2001; accepted in final form 24 May 2001
APS Manuscript Number A4-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001