Gritti A, Rosati B, Lecchi M, Vescovi A L, Wanke E
Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza, 2, I-20126, Italy.
Eur J Neurosci. 2000 Oct;12(10):3549-59. doi: 10.1046/j.1460-9568.2000.00234.x.
Although it is widely believed that astrocytes lack excitability in adult tissue, primitive action potential-like responses have been elicited from holding potentials negative to -80 mV, in cultured and injury-induced gliotic rodent astrocytes and in human glia under pathological conditions such as glioblastomas and temporal lobe epilepsy. The present study was designed to investigate the properties of astrocytes (identified by immunoreactivity for glial fibrillary acidic protein) derived from multipotent human embryonic CNS stem cells and cultured for 12-25 days in differentiating conditions. We describe here for the first time that brief (1 ms) current pulses elicit spikes from a resting potential (VREST) of approximately -37 mV and, more interestingly, that spontaneous firing can be occasionally recorded in human astrocytes. A voltage-clamp study revealed that in these cells: (i) the half-inactivation of the tetrodotoxin (TTX)-sensitive Na+ channels is around VREST; (ii) the delayed rectifier K+ current is very small; (iii) the ever-present transient outward A-type K+ channels are paradoxically capable of inhibiting the action potentials elicited from a negative membrane potential (-55 to -60 mV); and (iv) inwardly rectifying currents are not present. The responses predicted from a simulation model are in agreement with the experiments. As suggested by recent studies, the decrease of Na+ channel expression and the changes of the electrophysiological properties during the postnatal maturation of the CNS seem to exclude the possibility that astrocytes may play an excitable role in adult tissue. Our data show that excitability and firing should be considered an intrinsic attribute of human astrocytes during CNS development. This is likely to have physiological importance because the role of astrocytes during development is different from the [K+]o-buffering role played in adult CNS, namely the glutamate release and/or the guiding of migrating neurons.
尽管人们普遍认为星形胶质细胞在成体组织中缺乏兴奋性，但在培养的和损伤诱导胶质增生的啮齿动物星形胶质细胞以及处于诸如胶质母细胞瘤和颞叶癫痫等病理条件下的人类神经胶质细胞中，已从负于 -80 mV 的钳制电位诱发了类似原始动作电位的反应。本研究旨在探究源自多能人类胚胎中枢神经系统干细胞并在分化条件下培养 12 - 25 天的星形胶质细胞（通过胶质纤维酸性蛋白免疫反应性鉴定）的特性。我们在此首次描述，短暂（1 ms）的电流脉冲可从约 -37 mV 的静息电位（VREST）诱发尖峰，更有趣的是，在人类星形胶质细胞中偶尔可记录到自发放电。电压钳研究表明，在这些细胞中：（i）河豚毒素（TTX）敏感的 Na⁺通道的半失活电位约为 VREST；（ii）延迟整流 K⁺电流非常小；（iii）一直存在的瞬时外向 A 型 K⁺通道反常地能够抑制从负膜电位（-55 至 -60 mV）诱发的动作电位；（iv）不存在内向整流电流。模拟模型预测的反应与实验结果一致。正如最近的研究所表明的，中枢神经系统出生后成熟过程中 Na⁺通道表达的降低和电生理特性的变化似乎排除了星形胶质细胞在成体组织中可能发挥可兴奋作用的可能性。我们的数据表明，兴奋性和放电应被视为中枢神经系统发育过程中人类星形胶质细胞的固有属性。这可能具有生理重要性，因为星形胶质细胞在发育过程中的作用不同于其在成体中枢神经系统中所起的[K⁺]o缓冲作用，即谷氨酸释放和/或引导迁移神经元。
