AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 5 514-R521, Copyright © 1982 by American Physiological Society
Correlation of muscle activity with glycogen metabolism in muscle of Ascaris suum
M. J. Donahue, N. J. Yacoub and B. G. Harris
Isolated muscle segments from the parasitic roundworm Ascaris suum were
shown to contract when perfused with acetylcholine (ACh). The muscle
responded to ACh concentrations of 1 microM and was maximally contracted at
50 microM ACh. In fed muscle segments perfused with saturating levels of
ACh the glycogen synthase Ka values for glucose 6-phosphate increased from
0.5 to 0.95 mM. In starved segments stimulated by ACh, the muscle utilized
glycogen at a rate that was 1.41 micrograms.min-1.g tissue-1 greater than
the saline-perfused controls. The cyclic AMP (cAMP) levels remained
relatively constant at 0.34 +/- 0.08 nmol/g muscle during perfusion with
ACh. Contraction in the muscle could be inhibited in a dose-dependent
manner by gamma-aminobutyric acid (GABA). The presence of GABA in starved
muscle prevented the decrease in Ka values and phosphorylase activity
ratios brought about by glucose. Perfusion of GABA did not change cAMP
levels in the muscle. Starved muscle perfused with GABA utilized glycogen
at a rate that was 0.41 microgram.min-1.g-1 greater than saline-perfused
controls. The results indicated that muscle contraction could be elicited
by ACh, and that the energy for this process was derived from endogenous
glycogen stores, which were depleted during contraction. Muscle contraction
was also correlated with inactivation of glycogen synthase and activation
of phosphorylase. These processes appeared to function via a
cAMP-independent mechanisms.
