Bordey A, Lyons S A, Hablitz J J, Sontheimer H
Department of Neurobiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
J Neurophysiol. 2001 Apr;85(4):1719-31. doi: 10.1152/jn.2001.85.4.1719.
Neocortical freeze lesions have been widely used to study neuronal mechanisms underlying hyperexcitability in dysplastic cortex. Comparatively little attention has been given to biophysical changes in the surrounding astrocytes that show profound morphological and biochemical alterations, often referred to as reactive gliosis. Astrocytes are thought to aid normal neuronal function by buffering extracellular K(+). Compromised astrocytic K(+) buffering has been proposed to contribute to neuronal dysfunction. Astrocytic K(+) buffering is mediated, partially, by the activity of inwardly rectifying K(+) channels (K(IR)) and may involve intracellular redistribution of K(+) through gap-junctions. We characterized K(+) channel expression and gap-junction coupling between astrocytes in freeze-lesion-induced dysplastic neocortex. Whole cell patch-clamp recordings were obtained from astrocytes in slices from postnatal day (P) 16--P24 rats that had received a freeze-lesion on P1. A marked increase in glial fibrillary acidic protein immunoreactivity was observed along the entire length of the freeze lesion. Clusters of proliferative (bromo-deoxyuridine nuclear staining, BrdU+) astrocytes were seen near the depth of the microsulcus. Astrocytes in cortical layer I surrounding the lesion were characterized by a significant reduction in K(IR). BrdU-positive astrocytes near the depth of the microsulcus showed essentially no expression of K(IR) channels but markedly enhanced expression of delayed rectifier K(+) (K(DR)) channels. These proliferative cells showed virtually no dye coupling, whereas astrocytes in the hyperexcitable zone adjacent to the microsulcus displayed prominent dye-coupling as well as large K(IR) and outward K(+) currents. These findings suggest that reactive gliosis is accompanied by a loss of K(IR) currents and reduced gap junction coupling, which in turn suggests a compromised K(+) buffering capacity.
新皮质冷冻损伤已被广泛用于研究发育异常皮质中过度兴奋背后的神经元机制。相对而言，人们对周围星形胶质细胞的生物物理变化关注较少，这些星形胶质细胞表现出深刻的形态和生化改变，通常被称为反应性胶质增生。星形胶质细胞被认为通过缓冲细胞外钾离子（K(+)）来辅助正常的神经元功能。有人提出，星形胶质细胞对K(+)的缓冲能力受损会导致神经元功能障碍。星形胶质细胞对K(+)的缓冲部分是由内向整流钾通道（K(IR)）的活性介导的，并且可能涉及通过缝隙连接进行的K(+)的细胞内重新分布。我们对冷冻损伤诱导的发育异常新皮质中星形胶质细胞之间的K(+)通道表达和缝隙连接耦合进行了表征。从出生后第（P）16 - P24天、在P1时接受冷冻损伤的大鼠的脑片中的星形胶质细胞进行全细胞膜片钳记录。在冷冻损伤的整个长度上观察到胶质纤维酸性蛋白免疫反应性显著增加。在微沟深度附近可见增殖性（溴脱氧尿苷核染色，BrdU+）星形胶质细胞簇。损伤周围皮质层I中的星形胶质细胞的特征是K(IR)显著减少。微沟深度附近的BrdU阳性星形胶质细胞基本上不表达K(IR)通道，但延迟整流钾通道（K(DR)）的表达明显增强。这些增殖细胞几乎没有染料耦合，而与微沟相邻的过度兴奋区域中的星形胶质细胞显示出明显的染料耦合以及大的K(IR)和外向K(+)电流。这些发现表明，反应性胶质增生伴随着K(IR)电流的丧失和缝隙连接耦合的减少，这反过来表明K(+)缓冲能力受损。
