Amino acid production and translocation in incubated and superfused tissues from the brain.

Abstract

AbstractThe content of 12 amino acids in guinea pig cerebral cortical tissues was measured before and after incubation in glucose salines. The incubation caused reltively little change in tissue content, but induced a considerable production and accumulation of amino acids in the incubation medium. The dietarily essential amino acids, found in uncombined form, increased 3 to 6 fold. Glycine and alanine also increased; little change occurred in the quantity of free aspartic and glutamic acids. Amino acids were retained in the tissue in vitro against concentration gradients considerably higher than those estimated to obtain in vivo; by superfusing the tissue, the ratios were further increased. Electrical stimulation of the isolated tissues increased the amino acid accumulating in the medium during incubation, and increased the efflux of radioactive leucine during superfusion. Cycloheximide also increased the efflux of radioactive leucine during superfusion, while colchicine was found to decrease the proportion of total amino acid appearing in superfusates. Reasons are given for considering incubation fluids as artificial extensions of the interstitial fluid of the brain, and for regarding amino acid output from the tissue as a process counterbalancing axoplasmic flow.