Evidence from gene knockout studies implicates Asc-1 as the primary transporter mediating d-serine reuptake in the mouse CNS.
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 microm. The remaining uptake was mediated predominantly via a low affinity Na(+) dependent transporter with an IC(50) of 670 +/- 300 microm 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.
Rutter
A Richard
AR
Department of Molecular and Cellular Neuroscience, Merck Sharp and Dohme Research Laboratories, The Neuroscience Research Centre, Terlings Park, Harlow, Essex, UK. richard.a.rutter@gsk.com
Fradley
Rosa L
RL
Garrett
Elizabeth M
EM
Chapman
Kerry L
KL
Lawrence
Jason M
JM
Rosahl
Thomas W
TW
Patel
Smita
S
D027182:Amino Acid Transport System y+ / Q000172:deficiency* / Q000502:physiology*; D026905:Amino Acid Transport Systems / Q000172:deficiency / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D002490:Central Nervous System / Q000166:cytology / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004622:Embryo, Mammalian; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012694:Serine / Q000378:metabolism* / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism / Q000648:ultrastructure
D027182:Amino Acid Transport System y+; D026905:Amino Acid Transport Systems; C412624:Slc7a10 protein, mouse; D012694:Serine; D012964:Sodium