Interrelationship between the free energy change of ATP-hydrolysis, cytosolic inorganic phosphate and cardiac performance during hypoxia and reoxygenation.

Energy (ATP) dependent processes of the cell can in principle be divided into near equilibrium (high efficiency) processes, which depend on free energy (change) from ATP-hydrolysis and those not dependent on the free energy levels i.e. non-equilibrium processes. Due to the high efficiencies of the contractile process and the ion transport processes involved in excitation contracting coupling free energy dependence of these processes can be inferred. Though an apparent relationship between the free energy levels and performance can be observed in the early hypoxic failure and graded reoxygenation of isolated isometrically working rat hearts, EC-coupling alteration seem to preceed critical drop of free energy levels. These alterations appear not to be brought about by increasing cytosolic Pi. A pronounced negative staircase phenomenon in hypoxia accompanied by maintained free energy levels are interpreted in terms of a protective mechanism, which prevents critical drop of free energy levels of the cells at costs of their contractile performance.