抄録
In the cerebellum, four distinct types of glutamate transporters, GLAST, GLT-1, EAAC1 and EAAT4, are distributed especially near excitatory synapses in Purkinje cells (PCs). Glial transporters, GLAST and GLT-1, are co-localized in processes of Bergmann glia wrapping excitatory synapses on PCs, whereas neuronal transporters, EAAC1 and EAAT4, are expressed in extrasynaptic regions of PCs. To clarify differential roles of these transporters in the removal of synaptically released glutamate, we analyzed the kinetics of excitatory postsynaptic currents (EPSCs) in PCs in mice lacking either glial or neuronal transporter (the mice were kindly supplied by Dr. Kohichi Tanaka). GLAST contributed to uptake of glutamate that flooded out of the synaptic cleft at early times after transmitter release. It also played a critical role to maintain one-to-one relationship at the climbing fiber-PC synapses by preventing trans-cellular glutamate spillover. GLT-1 played a similar but minor role compared to GLAST. In contrast, the main role of EAAT4 was to remove low concentrations of glutamate that escaped from the uptake by glial transporters at late times and thus prevented the transmitter from spilling over to neighboring synapses in the same cell. Furthermore, it was intimately involved in the regulation of mGluR-mediated slow EPSCs induced by repetitive stimulation of parallel fibers. The contribution of EAAC1 to the removal of glutamate was almost negligible. [J Physiol Sci. 2008;58 Suppl:S126]
