Myoglobin supported oxygen consumption in isolated rat hearts under dysoxic conditions

Oxygen consumption was assessed in contracting, isolated rat hearts subjected to Langendorff perfusion. Initially, hearts were perfused with Krebs-Henseleit bicarbonate medium (KHB). Some hearts were treated with a 10 min pulse of medium containing 0.05 mM phenylhydrazine to oxidize approximately 78% of myoglobin to a state incapable of binding oxygen. Stepwise reduction in input PO2 resulted in a decline in oxygen consumption (MO2) in control and treated hearts. Phenylhydrazine treatment had no effect upon MO2 in hearts perfused with medium having a PO2 of about 585 mmHg or higher. However, at an input PO2 of approximately 370 mmHg, MO2 was decreased to 60% of the level at an input PO2 of 710 mmHg in untreated hearts and significantly lower to 32% of initial level in myoglobin blocked hearts. In subsequent experiments, hearts were perfused with KHB containing human red blood cells (RBCs) to elevate the oxygen content of the perfusate. The addition of RBCs to medium having a PO2 of approximately 140 mmHg resulted in enhancement of MO2 and maintenance of performance. But the preparations were considered to be dysoxic since MO2 with RBCs in the medium (PO2 approximately 140 mmHg) was lower than under perfusion with KHB (PO2 approximately 710 mmHg). This should however not detract from the utility of the model in elucidating myoglobin function under oxygen limiting conditions. At an input PO2 of 140 mmHg hearts treated with phenylhydrazine to impede myoglobin function had a significantly lower MO2 and viability than untreated hearts.(ABSTRACT TRUNCATED AT 250 WORDS)