ION CHANNELS IN SPINAL-CORD ASTROCYTES INVITRO .2. BIOPHYSICAL AND PHARMACOLOGICAL ANALYSIS OF 2 NA+ CURRENT TYPES
ION CHANNELS IN SPINAL-CORD ASTROCYTES INVITRO .2. BIOPHYSICAL AND PHARMACOLOGICAL ANALYSIS OF 2 NA+ CURRENT TYPES
复制标题
DOI：
10.1152/jn.1992.68.4.1001
复制
发表时间：
1992-10-01
影响因子：
2.5
通讯作者：
WAXMAN, SG
中科院分区：
文献类型：
--
作者：
SONTHEIMER, H;WAXMAN, SG
1.通过全细胞膜片钳记录研究脊髓培养的星形胶质细胞中表达的Na+电流。星形胶质细胞的两种亚型，即薄饼细胞和星状细胞，在形态上发生了分化，并显示出 Na+ 通道的表达密度对于神经胶质细胞来说异常高（2-8 个通道/mum2），并且与培养的神经元相当。2．就 Na+ 电流激活 (tau(m)) 和失活 (tau(h)) 时间常数而言，星状星形胶质细胞和薄饼星形胶质细胞中的 Na+ 电流与神经元 Na+ 电流相当，两种星形胶质细胞类型中的 Na+ 电流同样快。然而，它们在激活的电压依赖性方面有所不同，星状细胞中的电流-电压 (I-V) 曲线（-11.1 +/- 5.6 mV，平均值 +/- SD）比薄饼细胞（19.7 +/- 4.5 mV）高出约 10 mV。煎饼（平均 V1/2 = -48.8 mV）中的稳态激活（m（无穷大）曲线）比星状细胞（平均 V1/2 = -32.7 mV）负 16 mV。3。 Na+ 电流的稳态失活（h（无穷大）曲线）在两种星形胶质细胞类型中明显不同。在星状星形胶质细胞中h．曲线的中点接近 -65 mV (-64.6 +/- 6.5 mV)，与大多数培养的神经元相似。在煎饼星形胶质细胞中，h（无穷大）曲线为负-25 mV，中点接近-85 mV（84.5 +/- 9.5 mV）。4。这两种形式的 Na+ 电流还可以通过它们对河豚毒素 (TTX) 的敏感性来区分。星状星形胶质细胞中的 Na+ 电流对 TTX 高度敏感 [半最大抑制 (K(d)) = 5.7 nM]，而薄饼星形胶质细胞中的 Na+ 电流相对具有 TTX 抗性，需要 100 至 1,000 倍高浓度才能阻断 (K(d) = 1,007 nM)。5。 Na+ 电流由 Hodgkin-Huxley (HH) 模型拟合。在煎饼星形胶质细胞中，如在鱿鱼巨大轴突中，Na+电流动力学可以用m3h模型很好地描述，而在星状星形胶质细胞中，Na+电流可以用更高阶的激活幂项（m）更好地描述。平均而言，使用 m4h 模型获得了最佳拟合。6。薄饼星形胶质细胞能够在电流钳下产生动作电位（AP）样反应，而星状星形胶质细胞则不能。 AP 的 h（无穷大）曲线表明，需要比 -70 mV 更负的膜电位才能发生这些反应。由于细胞的静息电位去极化程度更高（-40 mV），稳态失活（h（无穷大）曲线）和静息电位之间的不匹配会导致 Ne 电流失活，不允许这些反应自发发生，并且使得体内脊髓煎饼星形胶质细胞不太可能发生 AP 样反应。 7。尽管星形星形胶质细胞中表达的Na+电流在所有特征上都与培养神经元中观察到的Na+电流相似，但在可兴奋细胞中尚未观察到负h（无穷大）曲线和表征煎饼星形胶质细胞中Na+电流的TTX不敏感性的组合，这表明这些细胞中存在星形胶质细胞特异性Na+通道。
1. Na+ currents expressed in astrocytes cultured from spinal cord were studied by whole cell patch-clamp recording. Two subtypes of astrocytes, pancake and stellate cells, were morphologically differentiated and showed expression of Na+ channels at densities that are unusually high for glial cells (2-8 channels/mum2) and comparable to cultured neurons.2. Na+ currents in stellate and pancake astrocytes were comparable to neuronal Na+ currents with regard to Na+-current activation (tau(m)) and inactivation (tau(h)) time constants, which were equally fast in both astrocyte types. However, they differed with respect to voltage dependence of activation, and current-voltage (I-V) curves were approximately 10 mV more positive in stellate cells (-11.1 +/- 5.6 mV, mean +/- SD) than in pancake cells (19.7 +/- 4.5 mV). Steady-state activation (m(infinity) curves) was 16 mV more negative in pancake (mean V1/2 = -48.8 mV) than in stellate cells (mean V1/2 = -32.7 mV).3. Steady-state inactivation (h(infinity) curves) of Na+ currents was distinctly different in the two astrocyte types. In stellate astrocytes h. curves had midpoints close to -65 mV (-64.6 +/- 6.5 mV), similar to most cultured neurons. In pancake astrocytes h(infinity)-curves were -25 mV more negative, with midpoints close to -85 mV (84.5 +/- 9.5 mV).4. The two forms of Na+ currents were additionally distinguishable by their sensitivity to tetrodotoxin (TTX). Na+ currents in stellate astrocytes were highly TTX sensitive [half-maximal inhibition (K(d)) = 5.7 nM] whereas Na+ currents in pancake astrocytes were relatively TTX resistant, requiring 100- to 1,000-fold higher concentrations for blockage (K(d) = 1,007 nM).5. Na+ currents were fit by the Hodgkin-Huxley (HH) model. In pancake astrocytes, as in squid gigant axons, Na+-current kinetics could be well described with an m3h model, whereas in stellate astrocytes Na+ currents were better described with higher-order power terms for activation (m). On average, best fits were obtained using an m4h model.6. Pancake astrocytes were capable of generating action-potential (AP)-like responses under current clamp whereas stellate astrocytes were not. The h(infinity) curve for APs shows that membrane potentials more negative than -70 mV are required to allow these responses to occur. Because the cells' resting potential was much more depolarized (-40 mV), this mismatch between the steady-state inactivation (h(infinity) curve) and resting potential, which results in Ne current inactivation, does not allow these responses to occur spontaneously and makes it unlikely that AP-like responses occur in spinal cord pancake astrocytes in vivo.7. Although Na+ currents expressed in stellate astrocytes resembled, in all their features, Na+ currents observed in cultured neurons, the combination of negative h(infinity) curve and TTX insensitivity characterizing Na+ currents in pancake astrocytes has not been observed in excitable cells, suggesting the existence of an astrocyte-specific Na+ channel in these cells.