Walz W
Department of Physiology, University of Saskatchewan, Saskatoon, Canada.
Glia. 2000 Aug;31(2):95-103. doi: 10.1002/1098-1136(200008)31:2<95::aid-glia10>3.0.co;2-6.
Since 1992, it has been possible to record ionic currents from identified astrocytes in situ, using brain slice technology. Brain slice recordings confirm previous in vitro findings that expression of voltage-gated K(+) and Na(+) channels are a feature of this cell type. In contrast to cultured astrocytes, most investigators found that astrocytes in situ did not contain detectable, or at very best only low, levels of glial fibrillary acidic protein (GFAP). Structural and immunocytochemical investigations determined that these cells are different from oligodendrocyte precursors. In addition to cells with this current pattern, many but not all investigators found a second pool of astrocytes with no voltage-gated ion channels and high GFAP content. These two subpopulations of cells were termed complex and passive astrocytes. The existence of passive astrocytes has been questioned because of possible problems with space clamp conditions and spillage of EGTA-buffered pipette solution around the cells before recordings. Another problem is the fact there is a discrepancy regarding the GFAP content of complex astrocytes. It is of interest that recent immunocytochemical studies suggest the existence of two pools of astrocytes, one with a high GFAP content and one with nondetectable GFAP. Given this, it is tempting to correlate the two (controversial) electrophysiological patterns with immunochemical differences (GFAP) in order to demonstrate two functionally discrete classes of astrocytes in adult gray matter. However, despite evidence that some of the K(+) channels may be involved in proliferation, the role of voltage-gated ion channels in this nonexcitable cell type remains unknown. This is despite the fact that astrocytic Na(+) channels show dramatic changes after pathological events, re-enforcing the notion that the expression of this channel is under tight neuronal control. Several studies suggest that there is a great degree of flexibility and that astrocytes can undergo rapid changes in expression of both membrane ion currents and GFAP. Although it is likely that astrocytes exhibit different structural and membrane properties, this heterogeneity might be a reflection of the flexible plasticity of one astrocyte type under influence of environmental factors rather than of the existence of two distinct and permanent subtypes.
自1992年以来，利用脑片技术已能够在原位记录特定星形胶质细胞的离子电流。脑片记录证实了先前体外研究的结果，即电压门控钾离子（K(+)）和钠离子（Na(+)）通道的表达是这种细胞类型的一个特征。与培养的星形胶质细胞不同，大多数研究人员发现原位星形胶质细胞不含可检测到的或至多仅含低水平的胶质纤维酸性蛋白（GFAP）。结构和免疫细胞化学研究确定这些细胞与少突胶质细胞前体不同。除了具有这种电流模式的细胞外，许多但并非所有研究人员还发现了第二类星形胶质细胞，它们没有电压门控离子通道且GFAP含量高。这两类细胞分别被称为复杂星形胶质细胞和被动星形胶质细胞。由于空间钳制条件可能存在的问题以及记录前EGTA缓冲的移液管溶液在细胞周围的泄漏，被动星形胶质细胞的存在受到了质疑。另一个问题是，关于复杂星形胶质细胞的GFAP含量存在差异。有趣的是，最近的免疫细胞化学研究表明存在两类星形胶质细胞，一类GFAP含量高，另一类GFAP检测不到。鉴于此，人们很想将这两种（有争议的）电生理模式与免疫化学差异（GFAP）联系起来，以证明成年灰质中存在两种功能上不同的星形胶质细胞类别。然而，尽管有证据表明一些钾离子通道可能参与增殖，但电压门控离子通道在这种非兴奋性细胞类型中的作用仍然未知。尽管星形胶质细胞的钠离子通道在病理事件后会发生显著变化，这进一步强化了该通道的表达受到神经元严格控制的观点。几项研究表明存在很大的灵活性，星形胶质细胞的膜离子电流和GFAP表达都可以快速变化。虽然星形胶质细胞可能表现出不同的结构和膜特性，但这种异质性可能反映了一种星形胶质细胞类型在环境因素影响下的灵活可塑性，而不是存在两种不同的永久亚型。
