The fish heart as a model system for the study of myoglobin.

A model is presented for myoglobin study based upon naturally occurring differences in myocardial myoglobin content in fish. The sea raven (Hemitripterus americanus) and the ocean pout (Macrozoarces americanus) have heart myoglobin contents of approx. 65 and 5 nmol/g wet wt, respectively. The maximal activities of enzymes associated with energy metabolism are similar in the two hearts. Isolated perfused hearts performed with similar efficiencies based upon similar rates of work, oxygen consumption and lactate production. Under normoxic perfusion conditions both hearts met 98% of the ATP demand by oxidative mechanisms. Myoglobin-rich sea raven hearts performed significantly better than myoglobin-poor ocean pout hearts under conditions of hypoxia and glycolytic blockage. The performance of sea raven hearts was impaired during hypoxia by decreasing the content of functional myoglobin with hydroxylamine. No effect upon performance was observed with the ocean pout heart. The data provide the first evidence that myoglobin plays a role in the maintenance of contractility in heart under hypoxic conditions.