[The oxygen dependence of the energy state of cardiac tissue--31P-NMR and optical measurement of myoglobin in perfused rat heart].

The relationship between the energy state and intracellular oxygen concentration was established in the cardiac tissues, where the former could be monitored by 31PNMR and latter by optical method for myoglobin absorption. The ratio of creatine phosphate to inorganic phosphate (PCr/Pi), started to fall at 40 microM ofintacellular oxygen concentration. In contrast, intracellular pH and cardiac function started to fall at 10 microM of oxygen. By infusion of epinephrine (0.01 micrograms/min), myoglobin was deoxygenated concomitant with the increase of left ventricular pressure and heart heart rate increased. The oxygen dependence of Parameters described above were unchanged by epinephrine infusion. Araki et al. reported that oxygen consumption, the reduction of pyridine nucleotide, the increase of lactate release started to change at 10 microM and reduction of cytochrome a + a3 started to increase at 40 microM. These results suggest that there is near-equilibrium state in the respiratory chain and oxidative phosphorylation in the cardiac tissue. The decrease of oxygen consumption was compensated by PCr/Pi ratio and cytochrome a + a3. And this near-equilibrium was maintained when the respiratory rate increased.