AJP - Cell Physiology, Vol 259, Issue 3 C409-C412, Copyright © 1990 by American Physiological Society
Influence of ATP turnover and metabolite changes on IMP formation and glycolysis in rat skeletal muscle
K. Sahlin, J. Gorski and L. Edstrom
Department of Clinical Physiology, Huddinge Hospital, Sweden.
Deamination of AMP to inosine monophosphate (IMP) and NH3 is thought to be
regulated by the observed increases in ADP, AMP, and H+. We have examined
this hypothesis by comparing the rate of IMP accumulation in contracting
and noncontracting rat skeletal muscle. The rate of IMP formation was high
during ischemic contraction, and consistent with previous studies,
formation of IMP was associated with high levels of muscle lactate,
depletion of phosphocreatine (PCr), and increased levels of ADP and AMP.
When the contraction period was followed by 5-min anoxic recovery, the
metabolic changes were maintained, but no further IMP or lactate was
formed. During long-term (2-4 h) anoxia, the rate of IMP formation was less
than 4% of that during contraction, despite similar changes in PCr,
lactate, ADP, and AMP. It is concluded that the observed changes in the
intracellular chemical environment are not sufficient to explain the high
rate of IMP formation during contraction but that a combination of
metabolic stress and a high ATP turnover rate is required. It is suggested
that a high ATP turnover rate during conditions of metabolic stress results
in transient increases in ADP and AMP at the site of ATP hydrolysis and
that these activate AMP deaminase and glycolysis. An alternative hypothesis
is that these processes are regulated by the increase in cytosolic Ca2+ in
a contracting muscle.
