Immunoisolation of GABA-specific synaptic vesicles defines a functionally distinct subset of synaptic vesicles

Synaptic vesicles from mammalian brain are among the best characterized tra fficking organelles. However, so far it has not been possible to characteri ze vesicle subpopulations that are specific for a given neurotransmitter. T aking advantage of the recent molecular characterization of vesicular neuro transmitter transporters, we have used an antibody specific for the vesicul ar GABA transporter (VGAT) to isolate GABA-specific synaptic vesicles. The isolated vesicles are of exceptional purity as judged by electron microscop y. Immunoblotting revealed that isolated vesicles contain most of the major synaptic vesicle proteins in addition to VGAT and are devoid of vesicular monoamine and acetylcholine transporters. The vesicles are 10-fold enriched in GABA uptake activity when compared with the starting vesicle fraction. Furthermore, glutamate uptake activity and glutamate-induced but not chlori de-induced acidification are selectively lost during immunoisolation. We co nclude that the population of GABA-containing synaptic vesicles is separabl e and distinct from vesicle populations transporting other neurotransmitter s.