Ca^(2+) Entry Through TRPC1 Channels Contributes to Intracellular Ca^(2+) Dynamics and Consequent Glutamate Release from Rat Astrocytes

各种不同的刺激作用于星型胶质细胞,可以导致胞浆内Ca2+浓度增加,进而释放更多谷氨酸作用于周边的神经元。大部分Ca2+来源于细胞内,小部分来源于细胞外。Ca2+内流是通过钙池操纵Ca2+通道(SOC)实现的。因此,作者观察在星型胶质细胞内Ca2+激活与谷氨酸释放过程中钙池操纵Ca2+通道(SOC)发挥了什么样的作用。已有研究显示星型胶质细胞所表达的TRPC通道(Ca2+通过瞬时受体电位通道相关蛋白)介导了钙池操纵Ca2+的内流。本文发现培养的星形胶质细胞以及从视皮质中新分离的星形胶质细胞表达TRPC1,TRPC4,和TRPC5。间接免疫组化显示这些蛋白存在于整个细胞中,然而机能检测TRPC1主要表达在质膜上。在新分离的星形胶质细胞中做标记,显示了在细胞发育过程中TRPC表达的改变。应用抗TRPC1的抗体,可以阻断TRPC1通道并且可以测定它们在培养的星形细胞的机械性和激动剂触发的钙离子内流过程中的作用。阻断TRPC1可以减少机械诱导的钙离子依赖性的谷氨酸盐的释放。这些实验数据表明,钙离子通过TRPC1通道的内流有助于钙离子在星形细胞中的信号传导以及由此引起的谷氨酸盐的释放。

Astrocytes can respond to a variety of stimuli by elevating their cytoplasmic Ca^2＋ concentration and can in turn release glutamate to signal adjacent neurons. The majority of this Ca^2＋ is derived from internal stores while a portion also comes from outside of the cell. Astrocytes use Ca^2＋ entry through store-operated Ca channels to refill their internal stores. Therefore, we investigated what role this store-operated Ca^2＋ entry plays in astrocytic Ca^2＋ responses and subsequent glutamate release. Astrocytes express canonical transient receptor potential （TRPC） channels that have been implicated in mediating store operated Ca^2＋ entry. Here, we show that astrocytes in culture and freshly isolated astrocytes from visual cortex express TRPC1 , TRPC4, and TRPC5. Indirect immunocytochemistry reveals that these proteins are present throughout the cell; the predominant expression of functionally tested TRPC1, however, is on the plasma membrane. Labeling in freshly isolated astrocytes reveals changes in TRPC expression throughout development. Using an antibody against TRPC1 we were able to block the function of TRPC1 channels and determine their involvement in mechanically and agonist-evoked Ca^2＋ entry in cultured astrocytes. Blocking TRPC1 was also found to reduce mechanically induced Ca^2＋ -dependent glutamate release. These data indicate that Ca^2＋ entry through TRPC1 channels contributes to Ca^2＋ signaling in astrocytes and the consequent gluta- mate release from these cells. 2008 Wiley-Liss, Inc.