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Transport characteristics of N ‐acetyl‐ l ‐aspartate in rat astrocytes: involvement of sodium‐coupled high‐affinity carboxylate transporter NaC3/NaDC3‐mediated transport system
Author(s) -
Fujita Takuya,
Katsukawa Hiromi,
Yodoya Etsuo,
Wada Miyuki,
Shimada Ayumi,
Okada Naoki,
Yamamoto Akira,
Ganapathy Vadivel
Publication year - 2005
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2005.03067.x
Subject(s) - transporter , sodium , chemistry , glutamate aspartate transporter , biochemistry , receptor , glutamate receptor , excitatory amino acid transporter , organic chemistry , gene
We investigated in the present study the transport characteristics of N ‐acetyl‐ l ‐aspartate in primary cultures of astrocytes from rat cerebral cortex and the involvement of NA + ‐coupled high‐affinity carboxylate transporter NaC3 (formerly known as NaDC3) responsible for N ‐acetyl‐ l ‐aspartate transport. N ‐acetyl‐ l ‐aspartate transport was NA + ‐dependent and saturable with a Michaelis–Menten constant ( K m ) of ∼110 µ m . NA + ‐activation kinetics revealed that the NA + to‐ N ‐acetyl‐ l ‐aspartate stoichiometry was 3 : 1 and concentration of Na + necessary for half‐maximal transport ( K NA m ) was 70 m m . NA + ‐dependent N ‐acetyl‐ l ‐aspartate transport was competitively inhibited by succinate with an inhibitory constant ( K i ) of 14.7 µ m , which was comparable to the K m value of NA + ‐dependent succinate transport (29.4 µ m ). l ‐Aspartate also inhibited NA + ‐dependent [ 14 C] N ‐acetyl‐ l ‐aspartate transport with relatively low affinity ( K i = 2.2 m m ), whereas N ‐acetyl‐ l ‐aspartate was not able to inhibit NA + ‐dependent aspartate transport in astrocytes. In addition, Li + was found to have a significant inhibitory effect on the NA + ‐dependent N ‐acetyl‐ l ‐aspartate transport in a concentration‐dependent manner. Furthermore, RT–PCR and western blot analyses revealed that NaC3 is expressed in primary cultures of astrocytes. Taken collectively, these results indicate that NaC3 expressed in rat cerebrocortical astrocytes is responsible for NA + ‐dependent N ‐acetyl‐ l ‐aspartate transport. This transporter is likely to be an essential prerequisite for the metabolic role of N ‐acetyl‐ l ‐aspartate in the process of myelination.