This study analyzes the importance of the source and rate of
ATP production (
glucose flux, glycogenolysis, and oxidative phosphorylation) in the prevention of
ischemic contracture in isolated rat hearts.
Ischemic contracture was initiated at about 10 minutes by
buffer perfusion with nonglycolytic substrates whereas the addition of 11 mM
glucose prevented
contracture for 2 hours. Tissue values of
ATP,
phosphocreatine, and
lactate could be dissociated from onset of
ischemic contracture. In hearts perfused with
acetate or
free fatty acid, with 11 mM
glucose, glycolytic
ATP production was 2.3-2.8 mumol/g fresh wt/min; as initial rates of glycogenolysis fell, glycolysis was maintained by a steady increase of
glucose flux to values in excess of 2 mumol
ATP/g fresh wt/min. Decreasing the
glucose flux by lowering the perfusate
glucose or by the addition of
2-deoxyglucose precipitated
ischemic contracture. When oxidative phosphorylation was further reduced by
hypoxia,
glucose still prevented
ischemic contracture; however, when oxidative phosphorylation dropped to near zero (near-anoxic) rates, glycolysis was inhibited, and
glucose could only delay
ischemic contracture to about 45 minutes. Combined
ATP production rates could be dissociated from
contracture. The metabolic parameter that correlated best with prevention or delay of
ischemic contracture was the rate of glycolytic flux from
glucose, which in this model of global low-flow
ischemia had to accelerate to provide a rate of
ATP production from
glucose in excess of 2 mumol/g fresh wt/min within 30 minutes of the start of
ischemia to prevent
ischemic contracture.