Functional membrane vesicles from the nervous system of insects. I. Sodium- and chloride-dependent gamma-aminobutyric acid transport.

(1) A synaptosomal fraction obtained from locust nervous tissue has been shown to possess an active gamma-aminobutyric acid transport mechanism. This activity is preserved and even enriched by the membrane vesicles derived from osmotically shocked synaptosomes. (2) Electron-microscopy examination indicates that the above membrane vesicles are derived predominantly from the neuronal plasma membrane and are devoid of any internal cellular organelles and components. Active transport of gamma-aminobutyric acid into these vesicles has been demonstrated with artificially imposed ion gradients as the sole energy source. (3) gamma-Aminobutyric acid transport can be driven by an Na+ gradient (out greater than in) and/or by a gradient of Cl- (out greater than in). This process is absolutely dependent on the simultaneous presence of both types of ion in the external medium. The stimulation of the process by valinomycin indicates that gamma-aminobutyric acid transport is an electrogenic process which is stimulated by a membrane potential (interior negative).