A reassessment of decreased amino acid accumulation by Ehrlich ascites tumor cells in the presence of metabolic inhibitors.

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Abstract
This study was undertaken to examine the mechanism by which metabolic inhibition reduces amino acid active transport in Ehrlich ascites mouse tumor cells. At 37.degree. C the metabolic inhibitor combination 0.1 mM 2,4-dinitrophenol (DNP) + 10 mM 2-deoxy-D-glucose (DOG) reduced the cell ATP concentration to 0.10-0.15 mM in < 5 min. This inhibition was associated with a 20.6% .+-. 6.4% (SD) decrease in the initial influx of .alpha.-aminoisobutyric acid (AIB), and a 2- to 4-fold increase in unidirectional efflux. These effects could be dissociated from changes in cell Na+ or K+ concentrations. Cells incubated to the steady state in 1.0-1.5 mM AIB showed an increased steady state flux in the presence of DNP + DOG. Steady state fluxes were consistent with trans-inhibition of AIB influx and trans-stimulation of efflux in control cells, but trans-stimulation of both fluxes in inhibited cells. In spite of the reduction of the cell ATP concentration to < 0.15 mM and greatly reduced transmembrane concentration gradients of Na+ and K+, cells incubated to the steady state in the presence of the inhibitors still established an AIB distribution ratio 13.8 .+-. 2.6. The results are interpreted to indicate that a component of the reduction of AIB transport produced by metabolic inhibition is attributable to other actions in addition to the reduction of cation concentration gradients. Reduction of cell ATP alone is not responsible for the effects of metabolic inhibition, and the transmembrane voltage and direct coupling to substrate oxidation via plasma membrane bound enzymes must be considered as possible energy sources for amino acid active transport.