AJP - Regulatory, Integrative and Comparative Physiology, Vol 237, Issue 5 291-R296, Copyright © 1979 by American Physiological Society
Reversal of phosphorylase activation in muscle despite continued contractile activity
R. K. Conlee, J. A. McLane, M. J. Rennie, W. W. Winder and J. O. Holloszy
During studies of the regulation of phosphorylase activity and
glycogenolysis in contracting muscle, it was found that conversion of
phosphorlyase beta to alpha is transient. Reversal of phosphorylase
activation during both continuous and intermittent stimulation in the
plantaris might, in part, have been due to development of fatigue. However,
a complete reversal of phosphorylase activation was also evident within 5
min in the absence of fatigue in soleus muscles stimulated tetanically with
100-ms-long trains at a rate of 60/min. These muscles showed no significant
decline in contractile force. Glycogen breakdown stopped in the soleus when
phosphorylase reverted to the beta form, providing evidence that
phosphorylase beta was not active. This lack of activity is probably
explained by the finding that ATP and AMP concentrations changed little,
while glucose 6-phosphate increased. Reversal of phosphorlyase activation
soon after the onset of steady-state work may be a mechanism for conserving
glycogen when the supply of other substrates is adequate to meet the
muscles' energy needs.
