The intracellular
glutamate concentration of oxygenated, isolated adult rat heart cells incubated with 0.15 mM
glutamate amounts to 2.89 +/- 0.6 mM. Under these conditions the velocity of
glutamate transport was 24.3 +/- 1.6 pmol.min-1.mg protein-1 and occurs via a high-affinity carrier characterized by an apparent affinity (K(m)) value of 0.18 +/- 0.03 mM. At high
glutamate concentrations ( > 1mM) this high-affinity transport system is superimposed by additional uptake processes of a low affinity but a high capacity for
glutamate. The 1.6-fold increased uptake of
glutamate observed during 30 min of anoxic incubation of cardiomyocytes does not prevent an intracellular decrease in this
amino acid to a concentration of 0.49 mM. After 15 min reoxygenation of cardiomyocytes the intracellular
glutamate content increases to the control values of oxygenated cells. Only 2.4% of the
glutamate increase after reoxygenation is due to the transport o
glutamate from the incubation medium. The competitive inhibitor of
transaminases,
aminooxyacetate, prevents both the observed intracellular decrease in
glutamate during
anoxia and the increase in intracellular
glutamate after reoxygenation of cardiomyocytes. Half of the amino groups needed for the synthesis of
glutamate originate from intracellular
alanine, which increases during
anoxia and is metabolized during reoxygenation of cardiomyocytes. The velocity of the
glutamate uptake of cardiomyocytes incubated in a medium containing 10 mM
L-glutamate amounted to 728 +/- 140 pmol.min-1.mg protein-1. During anoxic incubation of cardiomyocytes at this high extracellular
glutamate concentration, the intracellular
glutamate breakdown may be compensated by a simultaneous uptake of this
amino acid via the transport processes characterized by a high capacity