| Summary: | 碩士 === 國立陽明大學 === 神經科學研究所 === 101 === Oligodendrocyte precursor cells (OPCs), also known as NG2 cells, are glial cells that give rise to myelinating oligodendrocytes (OLs) in the central nervous system. Unlike other types of glial cells, OPCs receive synaptic inputs from neurons. However, synaptic integration in these non-neuronal cells remains poorly understood. We thus study voltage-gated K+ conductance, which may curtail synaptic potentials, in OPCs. Using electrophysiological and pharmacological approaches, we characterized functional and pharmacological properties of outward K+ currents in nucleated patches isolated from OPCs in the rat hippocampal CA1 area. Our results indicate that A-type Kv4 subunit is a major component of K+ channels in OPCs. We further correlated electrophysiological studies with single-cell RT-PCR analysis and immunochemistry to reveal subunit composition of K+ channels in OPCs. Interestingly, K+ currents are downregulated as the morphological features are more complex during the development of oligodencrocyte lineage cells. Further studies on passive membrane properties of OPCs show that these cells have a “leaky” membrane property with low specific membrane resistance (Rm), which is mediated by large Ba2+-sensitive K+ conductance at rest. Similar to Kv channels, passive membrane properties are also altered during development. To address the significance of K+ channels and passive membrane properties in signal processing in OPCs, we analyzed the realistic OPC cable models. The results revealed that large A-type, rather than delayed-rectifier type K+ conductance, substantially limits the EPSP integrations upon intense synaptic activation. Besides, a low Rm effectively narrows the time window for EPSP summation. As a result, Kv4 conductance and large resting K+ conductance differentially limit EPSP summation in OPCs.
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