Metabolic alterations associated with increased energy demand in fish white muscle

Effects of exercise stress on acid-base balance and respiratory function in blood of the teleost Tinca tinca

We measured the effects of severe, short-term exercise stress on the acid-base balance, the O2 transporting properties and the cofactors for O2 binding in the blood of tench, Tinca tinca. Short-term severe exercise resulted in a drastic decrease in arterial blood pH which is attributed to a mixed respiratory and metabolic acidosis. Concomitantly arterial PO2 rose in apparent compensation for the detrimental effects of the acidosis on O2 transport by the blood.

Goldfish muscle energy metabolism during electrical stimulation

Concentrations of key metabolites were determined in goldfish red muscle, while muscle and blood before and after direct electrical stimulation of the myotome (60 pulses/min, amplitude 500 mV, 10 msec pulse duration, during 10 min at 20 degrees C). In white muscle, levels of ATP, aspartate and adenylate energy charge are significantly lowered while those of AMP, IMP, NH3, alpha-ketoglutarate, lactate and malate are increased. In red muscle, the only change induced by stimulation is a 160% increase of the lactate level. In white muscle, IMP-accumulation and ammonia production are equal, suggesting the AMP-deaminase reaction to be the major source of muscular ammonia. Activation of white muscle adenylosuccinate synthetase and adenylosuccinase is suggested by the conversion of aspartate into malate during increased energy demand. There is no evidence of ammonia incorporation into alanine, glutamate or glutamine.

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.