Carbohydrate Is the Preferred Metabolic Fuel of the Hagfish (Myxine glutinosa) Heart

Abstract

Aerobic metabolism of Atlantic hagfish cardiac muscle was examined using an isolated electrically paced working preparation of systemic heart ventricle. Hagfish myocardium was shown to be capable of oxidizing both glucose and palmitic acid. The rate of D-glucose [14C-6] oxidation by the tissue was unaffected in the presence of 1 mM palmitic acid. Palmitic acid [14C-1] oxidation was significantly decreased in the presence of 5 mM D-glucose, indicating a distinct preference by the heart for aerobic metabolism of glucose. Mechanical performance of hagfish ventricles was maintained for 4 h in vitro when medium was supplemented with 5 mM D-glucose, or 2 mM pyruvate, or 5 mM lactate but decreased significantly when 1 mM palmitic acid was the sole exogenous fuel. Glycogen stores of the hagfish ventricle remain intact during over 4 h of paced work in vitro when incubated in the presence of 5 mM D-glucose but are reduced by nearly 50% in the presence of 1 mM palmitic acid alone. The carbohydrate-based metabolism of hagfish myocardium is fundamentally different from that of higher vertebrate taxa and may reflect the primitive position of cyclostome fish during vertebrate phylogeny.