Changed relation between phosphorylation potential and left ventricular developed pressure in guinea pig hearts during ischemia-reperfusion.

The concentrations of phosphocreatine and inorganic phosphate in the cytosol, the cytosolic pH, and the left ventricular developed pressure were measured in isolated guinea pig heart, before and during 35 min normothermic ischemia and during the reperfusion. The phosphorylation potential and its ratio to the left ventricular developed pressure were calculated. The ratio was increased after reperfusion, indicating a change in the regulation of energy supply and demand, with a relatively higher work efficiency at a lower phosphorylation potential. In fact, after 35 min ischemia, the left ventricular developed pressure recovered to 60 +/- 8%, while the phosphorylation potential recovered to 25 +/- 10% of their original values, whereas the heart rate returned to its pre-ischemic values. This apparent inconsistency is discussed in terms of an increased Ca2+ sensitivity of the contractile system after ischemia.