Roles of glutamate transporters in shaping excitatory synaptic currents in cerebellar Purkinje cells
Roles of glutamate transporters in shaping excitatory synaptic currents in cerebellar Purkinje cells
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DOI：
10.1111/j.1460-9568.2004.03224.x
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发表时间：
2004-03
影响因子：
3.4
通讯作者：
Y. Takayasu;M. Iino;S. Ozawa
中科院分区：
文献类型：
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作者：
Y. Takayasu;M. Iino;S. Ozawa
谷氨酸转运体的几种亚型在小脑浦肯野细胞的兴奋性突触附近大量表达。我们研究了谷氨酸转运蛋白在形成兴奋性突触后电流（EPSC）和使用谷氨酸转运蛋白的强效阻断剂dl-苏型-β-苄氧基天冬氨酸（dl-TBOA）调节小鼠小脑中细胞外谷氨酸水平中的作用。这种药物显著延长了通过刺激平行纤维和攀爬纤维诱发的浦肯野细胞中AMPA受体介导的EPSC。延长的EPSC的衰减相由双指数拟合，其中较慢的组分优先被AMPA受体的低亲和力竞争性拮抗剂γ-d-谷氨酰-甘氨酸抑制，表明由dl-TBOA诱导的较慢组分是由比导致EPSC峰值的浓度低的谷氨酸激活的AMPA受体介导的电流。这一结果表明，dl-TBOA阻止了突触释放的谷氨酸在突触间隙中的停留，并且还诱导谷氨酸溢出到突触外靶点以及邻近的突触。此外，在环噻嗪存在的情况下，高浓度的dl-TBOA在浦肯野细胞中产生连续的内向电流，其幅度达到攀爬纤维EPSC的峰值水平。这种连续的内向电流被AMPA受体阻断剂所消除，表明谷氨酸摄取的强烈抑制导致谷氨酸在细胞外空间的快速积累。这些结果突出了谷氨酸转运体在维持浦肯野细胞突触中的适当谷氨酸能传递中的重要性。
Several subtypes of glutamate transporters are abundantly expressed near the excitatory synapses on cerebellar Purkinje cells. We investigated the roles of the glutamate transporters in shaping the excitatory postsynaptic currents (EPSCs) and regulating the levels of extracellular glutamate in the mouse cerebellum using a potent blocker of glutamate transporters, dl‐threo‐β‐benzyloxyaspartate (dl‐TBOA). This drug markedly prolonged AMPA receptor‐mediated EPSCs in Purkinje cells evoked by stimulating both parallel fibres and climbing fibres. The decay phase of the prolonged EPSCs was fitted by double exponentials, of which the slower component was preferentially inhibited by a low‐affinity competitive antagonist of AMPA receptors, γ‐d‐glutamyl‐glycine, indicating that the slow component induced by dl‐TBOA was the AMPA receptor‐mediated current activated by lower concentrations of glutamate than those contributing to the peak of the EPSC. This result suggests that dl‐TBOA prolongs the stay of synaptically released glutamate in the synaptic cleft and also induces glutamate spillover to extrasynaptic targets as well as neighbouring synapses. Furthermore, high concentrations of dl‐TBOA in the presence of cyclothiazide generated a continuous inward current in Purkinje cells, of which the amplitude reached the peak level of the climbing‐fibre EPSC. This continuous inward current was abolished by the blocker of AMPA receptors, indicating that the strong inhibition of glutamate uptake causes the rapid accumulation of glutamate in the extracellular space. These results highlight the importance of glutamate transporters in maintaining the proper glutamatergic transmission in Purkinje cell synapses.