Freshly isolated astrocytes from rat hippocampus show two distinct current patterns and different [K+]o uptake capabilities
Freshly isolated astrocytes from rat hippocampus show two distinct current patterns and different [K+]o uptake capabilities
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DOI：
10.1152/jn.2000.84.6.2746
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发表时间：
2000-12-01
影响因子：
2.5
通讯作者：
Kimelberg, HK
中科院分区：
文献类型：
--
作者：
Zhou, M;Kimelberg, HK
星形胶质细胞是否在体内主要表达欧姆K+通道，以及不同K+通道的表达如何影响CNS中的[K+]（o）稳态一直是星形胶质细胞如何发挥功能的长期问题。在本研究中，我们解决了一些问题，在胶质细胞酸性蛋白[GFAP（+）]，新鲜分离的星形胶质细胞（FIA）从CA 1和CA 3区的P7-15大鼠海马。作为分离的，这些星形胶质细胞是解偶联的，允许更高分辨率的电生理学研究。FIA显示了两种不同的离子电流分布，两者都没有显示出纯粹的线性I-V关系。一个群体的星形胶质细胞有外向钾电流（I-Ka，I-Kd）和内向钠电流（I-Na）的组合表达。我们称这些外向整流星形胶质细胞（ORA）。另一种星形胶质细胞群体的特征在于相对对称的钾电流模式，包括外向I-Ka、I-Kd和丰富的内向钾电流（I-Kin），以及比奥拉斯更大的膜电容（C-m）和更负的静息膜电位（RMP）。我们称之为整流星形胶质细胞（弗拉）。70%的VRA中的I-Kin对Cs+基本不敏感，而其余30%的VRA中的I-Kin是敏感的。VRAs的I-Ka对4-氨基吡啶（4-AP）最敏感，而奥拉斯的I-Kdr对四乙基铵（TEA）最敏感。奥拉斯和VRA在分离自CA 1区的FIA中的发生率大致相等（52%奥拉斯对48% VRA），但奥拉斯在分离自CA 3区的FIA中富集（71%奥拉斯对29% VRA），表明海马内这两种类型的星形胶质细胞存在解剖学分离。VRA，而不是奥拉斯，响应于细胞外K+从5至10 mM的增加而显示出稳健的内向电流。RMP，R-in）原位转化为“被动星形胶质细胞”（即，这些显示线性I-V曲线），这种被动星形胶质细胞可能代表受原位广泛间隙-连接偶联影响的VRA。因此，我们的数据表明，至少在P7-15大鼠的CA 1和CA 3区，存在两类具有不同K+电流的GFAP（+）星形胶质细胞。只有VRA似乎适合于在生理膜电位下通过I-Kin通道摄取细胞外K+和增加[K+]（o）。奥拉斯表现出丰富的外向钾电流与更多的去极化RMP。因此，VRA和奥拉斯可能在体内分别协同摄取和释放K+。
Whether astrocytes predominantly express ohmic K+ channels in vivo, and how expression of different K+ channels affects [K+](o) homeostasis in the CNS have been long-standing questions for how astrocytes function. In the present study, we have addressed some of these questions in glial fibrillary acidic protein [GFAP(+)], freshly isolated astrocytes (FIAs) from CA1 and CA3 regions of P7-15 rat hippocampus. As isolated, these astrocytes were uncoupled allowing a higher resolution of electrophysiological study. FIAs showed two distinct ion current profiles, with neither showing a purely linear I-V relationship. One population of astrocytes had a combined expression of outward potassium currents (I-Ka, I-Kd) and inward sodium currents (I-Na). We term these outwardly rectifying astrocytes (ORA). Another population of astrocytes is characterized by a relatively symmetric potassium current pattern, comprising outward I-Ka, I-Kd, and abundant inward potassium currents (I-Kin), and a larger membrane capacitance (C-m) and more negative resting membrane potential (RMP) than ORAs. We term these variably rectifying astrocytes (VRA). The I-Kin in 70% of the VRAs was essentially insensitive to Cs+, while I-Kin in the remaining 30% of VRAs was sensitive. The I-Ka of VRAs was most sensitive to 4-aminopyridine (4-AP), while I-Kdr of ORAs was more sensitive to tetraethylammonium (TEA). ORAs and VRAs occurred approximately equally in FIAs isolated from the CA1 region (52% ORAs versus 48% VRAs), but ORAs were enriched in FIAs isolated from the CA3 region (71% ORAs versus 29% VRAs), suggesting an anatomical segregation of these two types of astrocytes within the hippocampus. VRAs, but not ORAs, showed robust inward currents in response to an increase in extracellular K+ from 5 to 10 mM. As VRAs showed a similar current pattern and other passive membrane properties (e.g., RMP, R-in) to "passive astrocytes" in situ (i.e., these showing linear I-V curves), such passive astrocytes possibly represent VRAs influenced by extensive gap-junction coupling in situ. Thus, our data suggest that, at least in CA1 and CA3 regions from P7-15 rats, there are two classes of GFAP(+) astrocytes which possess different K+ currents. Only VRAs seem suited to uptake of extracellular K+ via I-Kin channels at physiological membrane potentials and increases of [K+](o). ORAs show abundant outward potassium currents with more depolarized RMP. Thus VRAs and ORAs may cooperate in vivo for uptake and release of K+, respectively.