Active Transport of Amino-acid Across the Brain Cell Membrane

　When brain cortex slices were incubated aerobically in a saline medium in the presence of glucose as a substrate, amino-acids such as γ-aminobutyric acid（GABA），β-alanine，aspartic acid or D-，L-glutamic acid added were accumulated in the slices actively from the medium．If glutamate, an acidic amino-acid, was present in the medium in the concentration of 5 mM, the contents of intra-cellular water and potassium ions were increased markedly accompanied by the accumulation of glutamate．To the contrary，when GABA, a neutral amino-acid, was accumulated in the slices, there was very little change in the intracellular water and potassium content on a dry weight basis calculated by the chloride assumption．The evidence has been confirmed by electon-microscopic examination which indicated swelling of the nerve cells in the brain cortex．

　In potassium free medium, amino-acid transport was suppressed almost completely．However, GABA transport in the slices was augmented on omitting calcium ions from the medium or upon pyridoxal addition．The carrier system of GABA transportation across the cell membrane has been studied in relation to P³² turnover of phospholipid fractions in brain tissue．The incorporation of P³² into the phospholipids, particularly phosphatidic acid and phosphatidyl choline in the cytoplasmic particulates of brain tissue which are thought to be main structural elements of the nerve cell membrane, was greatly increased during the accumulation of GABA in the slices．This phenomenon has also been observed in a potassium rich medium which stimulated the metabolism of brain slices．Thus these phospholipids in cytoplasmic particulates might play an important part as carriers in the active transport across the brain cell membrane．