Evidence of glutathione transporter in rat brain synaptosomal membrane vesicles

Glutathione (GSH) transport was studied in synaptosomal membrane vesicles (SMV) of rat cerebral cortex. The present study shows that GSH uptake into SMV occurs very quickly in a time-dependent manner into an osmotically active intravesicular space. The initial rate of transport followed Michealis-Menten saturation kinetics with a Km 4.5+/-0.8 microM that shows a high affinity of the transporter for GSH. Therefore GSH uptake in SMV occurs by a mediated transport system which can be activated by either an inward gradient of cations, like Na+ or K+, or membrane depolarization. These results, together with those obtained by valinomycin-induced K+ diffusion potential, indicate that GSH synaptosomal transport is electrogenic by a negative charge transfer. The increase of GSH uptake measured by trans-stimulation experiments confirms a GSH bidirectional mediated transport which seems susceptible of modulation by changes in ionic fluxes and in the membrane potential. These results may indicate a possible involvement of this transporter in the role suggested for GSH in synaptic neurotransmission; also considering that GSH precursor of neuroactive aminoacids (glycine, glutamate), may contribute to regulate their level in synapses. Finally, a GSH transporter in synaptosomes may contribute to maintaining the GSH homeostasis in cerebral cortex, where decreases of GSH levels have been related to susceptibility to neuropathologies.