Active Transport of γ-Aminobutyricacid by Membrane Vesicles Isolated from Rat Brain

Membrane vesicles which are probably derived from synaptic plasma membranes have been isolated from rat brains. Active transport of γ-aminobutyric acid into these vesicles has been demonstrated with artificially imposed ion gradients as the sole energy source. This process can be driven either by a Na+ gradient (out > in) or by a gradient of any of a small number of small monovalent anions (out > in) of which chloride is by far the most effective. Transport of γ-aminobutyric acid was absolutely dependent on the simultaneous presence of both types of ions in the external medium. (2) Transport is inhibited about 50% by the proton ionophore carbonyl cyanide m-chlorophenylhydrazone and is enhanced up to twofold in those cases, in which K⁺-loaded vesicles are diluted into NaCl when valinomycin is present. Stimulations by SCN- were noted when the main driving force for transport was a Na⁺ gradient. This process thus appears to be an electrogenic process, which is stimulated by a membrane potential (interior negative). (3) The transport process, the K_m of which has been determined to be 2.5 μM, is strongly inhibited by ionophores able to collapse sodium gradients, such as nigericin and gramicidin. Also strong inhibition has been noted with chloropromazine, triphenyltin chloride, and p-hydroxymer-curibenzoate. In contrast transport was not affected by ouabain and only slightly inhibited by arsenate. (4) The results provide direct evidence for Na⁺-coupled active γ-aminobutyric acid transport by rat brain membrane vesicles. The anion dependence of the process is discussed.