CHARACTERISTICS OF CL--DEPENDENT L-[S-35]CYSTEIC ACID TRANSPORT INTO RAT-BRAIN SYNAPTIC MEMBRANE-VESICLES

Uptake of L-[S-35]cysteic acid (L-CA) in rat synaptic membrane vesicles was investigated. Preincubation with either 10 mM L-glutamic acid (L-Glu), 25 mM L-CA, 10 mM DL-homocysteic acid, or 25 mM DL-2-amino-4-phosphonobutyrate on membrane vesicles enhanced L-[S-35]CA and L-[H-3]Glu uptake. Na+ (5 mM) and omission of Cl- from the assay medium decreased L-[S-35]CA uptake into both 10 mM L-Glu-loaded and non-loaded membrane vesicles. The anion transport blockers, 4-acetamide-4'-isothiocyano-2,2'-disulfonic acid stilbene (SITS) and 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS), inhibited L-[S-35]CA uptake in a dose-dependent manner. The maximal uptake rate for L-[S-35]CA was decreased by 50-mu-M SITS, while the apparent Km value of L-CA was not changed. SITS increased the EC50 value of Cl- for L-[S-35]CA uptake from 5 mM to 10 mM with reduction of the maximal effect. These results suggested that L-[S-35]CA uptake into synaptic membrane vesicles was mediated by a SITS-sensitive hetero-exchange transport with non-labeled substrates.