Binding and Uptake of Amino Acids by Brain Tissue

(1) Of the endogenous glutamate, aspartate, alanine, glycine, and γ-aminobutyrate (GABA), 26–37% remains bound in particles when rat brain is homogenized in isosmotic salt-free sucrose solution; a smaller proportion, 16%, of the glutamine is bound. The amounts bound are increased if sodium chloride is present; the percentage increase is greatest in the case of GABA, followed by glutamate, and least with glutamine. When tracer amounts of radioactive amino acids are present in the solution in the absence of salt very little radioactivity appears in bound GABA or glutamine, but appreciable amounts are found in the other amino acids. In the presence of sodium chloride, the total amount of bound amino acid increases as does, to a lesser extent, the radioactivity bound. Ouabain and protoveratrine seem to cause some release of sodium-dependent binding of the amino acids; this is most marked with GABA.(2) Slices incubated in the presence of oxygen and glucose take up each of the amino acids when these are added t...