BOUND γ-AMINOBUTYRIC AND OTHER AMINO ACIDS IN BRAIN

Abstract

Previous work has shown that when brain is homogenized in saline medium, part of the γ-aminobutyric acid (GABA) in the tissue is found in free solution and part is bound or occluded in particulate material. In the present work it is shown that the GABA content of solid brain or anaerobic brain suspensions increases with time and the increase is all in the free form. In suspensions in the presence of oxygen and glucose no increase in GABA occurs. A lower proportion of the GABA is found in bound form if the suspension is prepared in the cold rather than at room or body temperature. The amount found in bound form is sharply dependent on pH. The optimum is about pH 7. If brain is homogenized in plain sucrose solutions, or if potassium is substituted for sodium in saline solution, the amount of bound GABA found is half that found in isosmotic sodium chloride. The normal amount remains bound if 10 mM sodium ion or 5 mM calcium ion is present in the sucrose solution. Glutamic acid, glutamine, alanine, and aspartic and acetylaspartic acids are also partly bound in brain. The amounts of these amino acids as well as of GABA found in brain frozen in situ are considerably lower than in brain which has been excised rapidly after death but without freezing.