Transport characteristics of N-acetyl-L-aspartate in rat astrocytes:: involvement of sodium-coupled high-affinity carboxylate transporter NaC3/NaDC3-mediated transport system
Transport characteristics of N-acetyl-L-aspartate in rat astrocytes:: involvement of sodium-coupled high-affinity carboxylate transporter NaC3/NaDC3-mediated transport system
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DOI：
10.1111/j.1471-4159.2005.03067.x
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发表时间：
2005-05-01
影响因子：
4.7
通讯作者：
Ganapathy, V
中科院分区：
文献类型：
--
作者：
Fujita, T;Katsukawa, H;Ganapathy, V
我们在本研究中研究了大鼠大脑皮层星形胶质细胞原代培养物中 N-乙酰-L-天冬氨酸的转运特性以及负责 N-乙酰-L-天冬氨酸转运的 NA(+) 偶联高亲和力羧酸转运蛋白 NaC3（以前称为 NaDC3）的参与。 N-乙酰基-L-天冬氨酸转运是NA(+)依赖性的并且可饱和，米氏常数(K-m)类似于110μM。NA(+)-激活动力学表明NA(+)与-N-乙酰基-L-天冬氨酸的化学计量比为3:1，半最大转运所需的Na+浓度(K-m(NA))为70 mM。 NA(+)依赖性的N-乙酰基-L-天冬氨酸转运被琥珀酸盐竞争性抑制，抑制常数(K-i)为14.7μM，与NA(+)依赖性的琥珀酸盐转运的Km值(29.4μM)相当。 L-天冬氨酸还以相对较低的亲和力 (K-i = 2.2 mM) 抑制 NA(+) 依赖性 [C-14] N-乙酰基-L-天冬氨酸转运，而 N-乙酰基-L-天冬氨酸不能抑制星形胶质细胞中 NA(+) 依赖性天冬氨酸转运。此外，Li+被发现对NA(+)依赖的N-乙酰基-L-天冬氨酸转运具有显着的抑制作用，且呈浓度依赖性。此外，RT-PCR 和蛋白质印迹分析表明 NaC3 在星形胶质细胞的原代培养物中表达。总的来说，这些结果表明大鼠大脑皮质星形胶质细胞中表达的 NaC3 负责 NA(+) 依赖性 N-乙酰基-L-天冬氨酸转运。这种转运蛋白可能是 N-乙酰基-L-天冬氨酸在髓鞘形成过程中发挥代谢作用的重要先决条件。
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 similar to 110 mu 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-m(NA)) was 70 mM. NA(+)-dependent N-acetyl-L-aspartate transport was competitively inhibited by succinate with an inhibitory constant (K-i) of 14.7 mu M, which was comparable to the Km value of NA(+)-dependent succinate transport (29.4 mu M). L-Aspartate also inhibited NA(+)-dependent [C-14] N-acetyl-L-aspartate transport with relatively low affinity (K-i = 2.2 mM), 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.