| Project/Area Number |
62490020
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
広領域
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| Research Institution | KYUSHU INSTITUTE OF TECHNOLOGY (1988)
Okazaki National Research Institutes (1987) |
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Principal Investigator |
YASUI Syozo Kyushu Institute of Technology, Department of Control Engineering and Science, Professor, 情報工学部, 教授 (50132741)
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| Co-Investigator(Kenkyū-buntansha) |
KANEKO Akimichi National Institute for Physiological Sciences, Professor, 生理学研究所, 教授 (00051491)
立花 政夫 岡崎国立共同研究機構, 生理学研究所, 助手 (60132734)
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| Project Period (FY) |
1987 – 1988
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| Project Status |
Completed (Fiscal Year 1988)
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| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1988: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1987: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Keywords | Ca channel / Na-Ca exchange / Na-K ATPase / homeostasis / horizontal cells / retina / vision / 視覚 / ニューロン / Na-Ca交換 / Na-Kポンプ / 細胞内Ca貯蔵庫 / ケモスタシス / カルシウムチャンネル / NaーK ATPase / 細胞内Ca濃度 / カフェイン |
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| Research Abstract |
Excitation of neuronal and muscular cells is triggered by depolarization-induced Ca^<2+> entry to the cytoplasm. The release of neurotransmitter substance from presynaptic terminals is mediated by similar mechanisms. As such, Ca^<2+> is an internal messenger, with its cytosolic concentration normally maintained at the submicromolar level. The Ca buffering can be subserved by cytoplasmic ca ion stores. No less important for the Ca regulation is the Na-Ca exchange machinery that excludes calcium ions by letting Na ions move into the cell. The passive Na influx may also result from voltage-gated as well as drug-operated channels. Thus. Na ions also need to be expelled. This physiologic demand is fulfilled by the Na-K pump. This study was done in the context of intracellular ion homeostasis recaputulated above.
Voltage clamp experiments using patch pippete were made on solitary horizontal cells isolated enzymatically from the goldfish retina. Since the physiological dynamic range of these non-spiking second-order visual neurons overlaps the membrane voltage region that activates the voltage-gated Ca channel, some mechanism needs to exist to drive out Ca ions. A series of experiments involving the Co test and Na-free substitution showed that the Ca extrusion is subserved by the Na-Ca exchanger. Another set of experiments including by caffeine application indicated the presence of internal calcium stores having a storage capacity of as much as several mM. In this regard, the endplasmic reticulum probably plays a major role. Some regulatory system is required with respect to Na ions as well, to compensate for three types of Na influx: TTX-sensitive one, the Na-Ca exchange component and synaptic current mediated by an excitatory neurotransmitter from photoreceptor terminals. the Ns-KATP ase ope rates for this requirement. Evidence being provided by an ouabain experiment.
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