The anaerobic heart: succinate formation and mechanical performance of cat papillary muscle

Quiescent or paced, isometrically contracting right ventricular papillary muscles of cat heart were incubated under oxygenated or hypoxic (Po2 less than 10 Torr) conditions in order to investigate lactate and succinate formation. Both compounds were produced and released into the incubation medium during oxygen deficiency. Mechanical performance stimulated synthesis of both compounds under hypoxic as well as oxygenated conditions. Pacing led to the accumulation of large amounts of glutamine both under oxygenated and hypoxic conditions. Hypoxia resulted in a marked depletion of high-energy phosphates and concomitantly mechanical performance was impaired, i.e. developed tension fell rapidly and relaxation rate decreased. Supplying hypoxic, contracting muscles with aspartate (2 mM) resulted in maintenance of muscular function to some extent and led to augmented release of succinate and lactate. The data indicate that anaerobic succinate formation is correlated to the energy requiring processes of the myocardium. Maintenance of myocardial function by the supply of amino acids may be related to their conversion into succinate and to the stimulation of glycolysis.