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Evidence from gene knockout studies implicates Asc‐1 as the primary transporter mediating d ‐serine reuptake in the mouse CNS
Author(s) -
Rutter A. Richard,
Fradley Rosa L.,
Garrett Elizabeth M.,
Chapman Kerry L.,
Lawrence Jason M.,
Rosahl Thomas W.,
Patel Smita
Publication year - 2007
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.2007.05446.x
Subject(s) - serine , reuptake , transporter , forebrain , chemistry , glycine , neurotransmitter transporter , knockout mouse , biochemistry , microbiology and biotechnology , biology , receptor , amino acid , endocrinology , central nervous system , gene , serotonin , phosphorylation
In the mammalian central nervous system, transporter‐mediated reuptake may be critical for terminating the neurotransmitter action of d ‐serine at the strychnine insensitive glycine site of the NMDA receptor. The Na + independent amino acid transporter alanine–serine–cysteine transporter 1 (Asc‐1) has been proposed to account for synaptosomal d ‐serine uptake by virtue of its high affinity for d ‐serine and widespread neuronal expression throughout the brain. Here, we sought to validate the contribution of Asc‐1 to d ‐serine uptake in mouse brain synaptosomes using Asc‐1 gene knockout (KO) mice. Total [ 3 H] d ‐serine uptake in forebrain and cerebellar synaptosomes from Asc‐1 knockout mice was reduced to 34 ± 5% and 22 ± 3% of that observed in wildtype (WT) mice, respectively. When the Na + dependent transport components were removed by omission of Na + ions in the assay buffer, d ‐serine uptake in knockout mice was reduced to 8 ± 1% and 3 ± 1% of that measured in wildtype mice in forebrain and cerebellum, respectively, suggesting Asc‐1 plays a major role in the Na + independent transport of d ‐serine. Potency determination of d ‐serine uptake showed that Asc‐1 mediated rapid high affinity Na + independent uptake with an IC 50 of 19 ± 1 µ m . The remaining uptake was mediated predominantly via a low affinity Na + dependent transporter with an IC 50 of 670 ± 300 µ m that we propose is the glial alanine–serine–cysteine transporter 2 (ASCT2) transporter. The results presented reveal that Asc‐1 is the only high affinity d ‐serine transporter in the mouse CNS and is the predominant mechanism for d ‐serine reuptake.