Abstract
N-Acetylaspartate is a highly specific marker for neurons and is present at high concentrations in the central nervous system. It is not present at detectable levels anywhere else in the body other than brain. Glial cells express a high-affinity transporter for N-acetylaspartate, but the molecular identity of the transporter has not been established. The transport ofN-acetylaspartate into glial cells is obligatory for its intracellular hydrolysis, a process intimately involved in myelination.N-Acetylaspartate is a dicarboxylate structurally related to succinate. We investigated in the present study the ability of NaDC3, a Na+-coupled high-affinity dicarboxylate transporter, to transport N-acetylaspartate. The cloned rat and human NaDC3s were found to transportN-acetylaspartate in a Na+-coupled manner in two different heterologous expression systems. The Michaelis-Menten constant for N-acetylaspartate was ∼60 μM for rat NaDC3 and ∼250 μM for human NaDC3. The transport process was electrogenic and the Na+:N-acetylaspartate stoichiometry was 3:1. The functional expression of NaDC3 in the brain was demonstrated by in situ hybridization and reverse transcription-polymerase chain reaction as well as by isolation of a full-length functional NaDC3 from a rat brain cDNA library. In addition, the expression of a Na+-coupled high-affinity dicarboxylate transporter and the interaction of the transporter withN-acetylaspartate were demonstrable in rat primary astrocyte cultures. These studies establish NaDC3 as the transporter responsible for the Na+-coupled transport ofN-acetylaspartate in the brain. This transporter is likely to be an essential component in the metabolic role ofN-acetylaspartate in the process of myelination.
Footnotes
-
Send reprint requests to: Vadivel Ganapathy, Ph.D., Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2100. E-mail: vganapat{at}mail.mcg.edu
-
↵1 This study was supported by National Institutes Health Grants DA 10045 and HD 33347.
- Abbreviations:
- NaDC
- Na+-coupled dicarboxylate transporter
- HRPE
- human retinal pigment epithelial
- PDC
- trans-pyrrolidine-2,4-dicarboxylate
- NMDG
- N-methyl-d-glucamine
- kbp
- kilobase pairs
- RT-PCR
- reverse transcription-polymerase chain reaction
- Received January 26, 2000.
- Accepted June 2, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|