@misc{oai:ir.soken.ac.jp:00001457, author = {李, 海雄 and リ, ヘウン and LEE, Hae Ung}, month = {2016-02-17, 2016-02-17}, note = {Astrocytes, the major glial cell type in the CNS, have been considered to be passive bystanders that merely provide support to neuronal networks. However astrocyte is now recognized as one of the active elements that directly modulate brain functions. Astrocytes sense and integrate synaptic activity and, depending on intracellular Ca²⁺ levels, release gliotransmitters (e.g. glutamate, ATP and D-serine) that have feedback actions on neurons. Although these reports provided clues that astrocytes are the active components in the brain, they did not analyze the temporal and spatial pattern of gliotransmitters release from astrocytes. To examine the release of gliotransmitters, such as ATP and glutamate, he applied imaging techniques visualizing ATP and glutamate released from astrocytes.
　　　Luciferin-luciferase solution was applied to the extracellular fluid of astrocytes to visualize ATP release. To visualize glutamate release, glutamate optic sensor (EOS) was applied. This specific probe for detecting glutamate is a hybrid molecule consisting of glutamate-binding protein (AMPA receptor GluR2 subunit extracellular domain as a glutamate-binding protein) and a small-molecule fluorescent dye. He successfully observed ATP or glutamate release from astrocytes and applied these technologies to observe spatial and temporal pattern of gliotransmitters release.
　　　Many researchers found that the astrocytic intracellular calcium responses are co-related with the functions of astrocytes. To reveal the significance of intracellular calcium elevation of astrocytes on the gliotransmitter release, he tried to obtain the spatio-temporal information using these technologies combined with the calcium imaging technology. By ATP (1 μM or higher) stimulation, intracellular calcium elevation was observed in all astrocytes. However, under the same condition, only few(ca.3?7%) released glutamate. A similar phenomenon was observed in glutamate-evoked ATP release from astrocytes; even though all astrocytes showed increased intracellular calcium levels, small proportion of astrocytes released ATP by glutamate stimulation (ca. 1%). It was expected that astrocytes which showed intracellular calcium elevation release gliotransmitters, however, my results were totally different.
　　　Pharmacological approaches revealed that P2X and P2Y receptors showed different patterns of intracellular calcium elevation, however, a similar pattern of glutamate release was evoked by P2X and P2Y stimulations. For the glutamate stimulation, it was suggested that the subtype 5 of metabotrophic glutamate receptor was responsible to increase intracellular calcium in astrocytes and to release ATP from astrocytes. The glutamate stimulation evoked calcium waves among astrocytes, and then astrocytes released ATP around 200 seconds after glutamate application.
　　　His experiments using cultured astrocytes revealed following things: 1) intracellular calcium elevation was not enough to evoke gliotransmitter release, 2) direct relationship between glutamate release and intracellular calcium elevation evoked by ATP stimulation is low, 3) ATP release evoked by glutamate stimulation had relevance to the intracellular calcium elevation which represent the activation of astrocytes. For the first time, glitransmitter release was successfully visualized and the mechanisms of gliotransmitter release were revealed through these imaging technologies., application/pdf, 総研大甲第1263号}, title = {Physiological significance of ATP and glutamate release from astrocytes}, year = {} }