Lipopolysaccharide-induced down-regulation of Ca2+ release-activated Ca2+ currents (ICRAC) but not Ca2+-activated TRPM4-like currents (ICAN) in cultured mouse microglial cells
Lipopolysaccharide-induced down-regulation of Ca2+ release-activated Ca2+ currents (ICRAC) but not Ca2+-activated TRPM4-like currents (ICAN) in cultured mouse microglial cells
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DOI：
10.1113/jphysiol.2007.145151
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发表时间：
2008-01-15
影响因子：
5.5
通讯作者：
Fleig, Andrea
中科院分区：
文献类型：
--
作者：
Beck, Andreas;Penner, Reinhold;Fleig, Andrea
小胶质细胞是哺乳动物中枢神经系统的主要免疫活性细胞。培养的小胶质细胞的激活和随后一氧化氮和细胞因子的释放关键取决于细胞内钙水平。由于小胶质细胞在中枢神经系统的病理事件中经历了戏剧性的形态、生化和电生理变化，我们研究了参与细胞钙稳态的离子通道在培养的小鼠皮质小胶质细胞中表达水平的时间变化。具体地说，我们评估了未激活的小胶质细胞和暴露于脂多糖(LPS)激活的细胞中的内向和延迟外向整流钾电流(I-irk和i-DRK)、钙(Ca~(2+)释放激活的Ca~(2+)电流(I-CRAC)和Ca~(2+)激活的TRPM4样电流(I-CAN)。在培养的前3天，细胞的大小和形状保持不变，但表现为明显的I-IRK的细胞比例上升，表达I-DRK的细胞比例下降。保留I-DRK的细胞表现出较小的波幅，而I-IRK和I-CRAC的波幅不受影响。然而，1mgml(-1)的内毒素作用24 h后，大多数细胞呈现阿米巴(‘煎蛋’状)形态，细胞电容增加62%。在那个时间点，只有14%的细胞表达I-irk，3%的细胞单独表达i-DRK，而大多数细胞同时表达这两种电流。I-CRAC和I-IRK的波幅在刺激后逐渐降低，而I-DRK的波幅在刺激后6h达到最大值，然后恢复到刺激前的表达水平。培养的小胶质细胞也出现TRPM4样钙激活的非选择性电流(I-CAN)，其EC50为1.2mM[Ca~(2+)](I)。该电流的表达水平在内毒素暴露期间和24 h后均无明显变化。我们认为，内毒素诱导的I-IRK和I-CRAC的下调将降低细胞在受体激活时产生显着钙内流的能力，并导致对外部刺激的敏感性降低。在这种情况下，I-CaN的表达将保持不变，尽管由于细胞的钙内流能力减弱，其活性将自动降低。
Microglia are the main immunocompetent cells of the mammalian central nervous system (CNS). Activation of cultured microglial cells and subsequent release of nitric oxide and cytokines critically depends on intracellular calcium levels. Since microglia undergo dramatic morphological, biochemical and electrophysiological changes in response to pathological events in the CNS, we investigated temporal changes in expression levels of ion channels involved in cellular calcium homeostasis in mouse cortical microglial cells in culture. Specifically, we assessed the inward and delayed outward rectifier potassium currents (I-IRK and I-DRK), calcium (Ca2+) release-activated Ca2+ currents (I-CRAC) and Ca2+-activated TRPM4-like currents (I-CAN) in non-activated microglia and cells that were activated by exposure to lipopolysaccharide (LPS) between 3 and 48 h. Unstimulated microglial cells, subcultured from an astrocyte coculture, typically exhibited a ramified, rod-shaped morphology. During the first 3 days of culture cell size and shape were maintained, but the percentage of cells showing prominent I-IRK went up and those expressing I-DRK went down. Cells retaining I-DRK exhibited smaller amplitudes, whereas those Of I-IRK and I-CRAC were not affected. However, after 24 h of exposure to 1 mu g ml(-1) LPS, most cells showed an amoeboid ('fried egg'-shaped) morphology with a 62% increase in cell capacitance. At that point in time, only 14% of the cells revealed I-IRK and 3% had I-DRK exclusively, whereas the majority of cells expressed both currents. The amplitudes of I-CRAC and I-IRK progressively decreased after stimulation, whereas I-DRK transiently reached a maximum after 6 h of LPS exposure and then returned to pre-stimulation expression levels. Cultured microglia also revealed TRPM4-like, Ca2+-activated non-selective currents (I-CAN) with an EC50 of 1.2 mu M [Ca2+](i). The expression levels of this current did not change significantly during and after 24 h of LPS exposure. We propose that LPS-induced down-regulation of I-IRK and I-CRAC will reduce the cell's capacity to produce significant calcium influx upon receptor activation and result in decreased sensitivity to exogenous stimulation. In this scenario, I-CAN expression would remain constant, although its activity would automatically be reduced due to the diminished calcium influx capacity of the cell.