1H nuclear magnetic resonance studies of sarcoplasmic oxygenation in the red cell-perfused rat heart.

The proximal histidine N delta H proton of deoxymyoglobin experiences a large hyperfine shift resulting in its 1H nuclear magnetic resonance (NMR) signal appearing at approximately 76 ppm (at 35 degrees C), downfield of the diamagnetic spectral region. 1H NMR of this proton is used to monitor sarcoplasmic oxygen pressure in isolated perfused rat heart. This method monitors intracellular oxygenation in the whole heart and does not reflect oxygenation in a limited region. The deoxymyoglobin resonance intensity is reduced upon conversion of myoglobin to the ferric form by sodium nitrite. 1H resonances of the N delta H protons of the alpha and beta subunits of bovine deoxyhemoglobin do not interfere with the measurement of myoglobin deoxygenation in blood-perfused rat heart. We find that steady-state myoglobin deoxygenation is increased progressively (and reversibly) as oxygenation of the perfusing medium is decreased in both saline and red blood cell-perfused hearts at constant work output. An eightfold increase in the heart rate of the blood-perfused heart resulted in no change in the deoxymyoglobin signal intensity. Intracellular PO2 of myoglobin-containing cells is maintained remarkably constant in changing work states.