AMINO ACID TRANSPORT IN BRAIN CORTEX SLICES: III. THE UTILIZATION OF ENERGY FOR TRANSPORT

Abstract

When rat brain cortex slices are incubated with amino acids in the presence of various sugars, the ratio of amino acid transported to the steady-state level of ATP (termed the transport quotient) is constant. The actual amount of ATP maintained is greatest with glucose and mannose but somewhat less with fructose and galactose. Certain α-keto acids (pyruvate, oxalacetate, α-ketoglutarate, or glutamate which can give rise to α-ketoglutarate) also support glycine transport but with a lesser efficiency. Fumarate, malate, and succinate have little ability to support amino acid transport.The transport supported by pyruvate is particularly resistant to the action of agents which markedly reduce the transport supported by glucose as substrate. These agents include dinitrophenol, digoxin, and uranyl ions. Inhibitory effects are obtained with high concentrations of potassium ions whether the substrate is glucose or pyruvate.These results are interpreted in terms of pyruvate dismutation and acetate thiokinase leading to ATP production and in terms of intracellular localization of ATP.