Amino acid stimulation of oxygen and substrate utilization by cardiac myocytes

The inclusion of plasma levels of the natural amino acids plus 2.5 mM glutamate and 2.5 mM malate (PAAGM) raised the oxygen consumption and glucose oxidation of isolated cardiac myocytes in phosphate buffered saline. The addition of calcium (1.25 mM) and magnesium (0.66 mM) potentiated the stimulatory effect of PAAGM on glucose oxidation and oxygen consumption, PAAGM did not alter the shape of the dose-response curve for glucose oxidation by the isolated cardiac myocyte preparation. It did increase the amount of glucose oxidation at any given media glucose concentration up to 20 mM. PAAGM also increased the rate of lactate oxidation by the isolated cardiac myocyte preparation. PAAGM did not stimulate the oxidation of octanoate unless there was glucose present in the incubation media as well. Measurements of the concentrations of free amino acids indicated higher levels in myocytes incubated in PAAGM than in myocytes incubated in phosphate buffered saline. The data suggest that substrate metabolism by the isolated cardiac myocyte preparation can be influenced by the presence of plasma constituents that would be available to the myocardium in vivo.