Characteristics of Cl−-dependentl-35Scysteic acid transport into rat brain synaptic membrane vesicles

摘要

Uptake ofl-35Scysteic acid (L-CA) in rat synaptic membrane vesicles was investigated. Preincubation with either 10 mMl-glutamic acid (L-Glu), 25 mM L-CA, 10 mMdl-homocysteic acid, or 25 mMdl-2-amino-4-phosphonobutyrate on membrane vesicles enhanced L-35SCA and L-3HGlu uptake. Na+(5 mM) and omission of Cl−from the assay medium decreased L-35SCA 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 stibene (SITS) and 4,4′-diisothiocyano-2,2′-disulfonic acid stilbene (DIDS), inhibited L-35SCA uptake in a dose-dependent manner. The maximal uptake rate for L-35SCA was decreased by 50 μM SITS, while the apparent Km value of L-CA was not changed. SITS increased the EC50value of Cl−for L-35SCA uptake from 5 mM to 10 mM with reduction of the maximal effect. These results suggested that L-35SCA uptake into synaptic membrane vesicles was mediated by a SITS-sensitive hetero-exchange transport with non-labele