Robert A, Magistretti P J
Département de Pharmacologie, Centre Médical Universitaire, Genève, Switzerland.
Glia. 1997 May;20(1):38-50.
Cultured mouse cortical astrocytes of the stellate type were studied by using the patch-clamp technique in whole-cell configuration. The astrocytes express at least two types of outwardly rectifying K+ channels which mediate a transient and a sustained current. Activation of AMPA receptors by kainate leads to a substantial blockade of both types of K+ currents. The blockade is absent when Na+ is withdrawn from the external medium, suggesting that it is caused by constant Na+ influx through AMPA receptors. The presence of high Na+ solutions in the pipette induces a blockade of both K+ currents which is very similar to the blockade induced by kainate, supporting thus the view that the mechanism of the blockade of K+ channels by kainate involves Na+ increases in the submembrane area. The blockade occurs between 20 and 40 mM [Na+]i, which is within the physiological range of [Na+]i in astrocytes. The data may suggest that the blockade of K+ channels by high [Na+]i conditions could provide a mechanism to prevent K+ leakage from the astrocytes into the extracellular space during periods of intense neuronal activity.
采用膜片钳技术的全细胞记录模式，对培养的星型小鼠皮层星形胶质细胞进行了研究。星形胶质细胞表达至少两种外向整流钾离子通道，介导瞬时电流和持续电流。用红藻氨酸激活AMPA受体可导致这两种钾离子电流的显著阻断。当从外部介质中去除钠离子时，这种阻断作用消失，表明它是由通过AMPA受体的持续钠离子内流引起的。移液管中存在高钠溶液会导致两种钾离子电流的阻断，这与红藻氨酸诱导的阻断非常相似，因此支持了红藻氨酸阻断钾离子通道的机制涉及细胞膜下区域钠离子增加的观点。这种阻断发生在细胞内钠离子浓度为20至40 mM之间，这在星形胶质细胞内钠离子浓度的生理范围内。这些数据可能表明，在强烈神经元活动期间，高细胞内钠离子浓度条件下钾离子通道的阻断可能提供一种机制，以防止钾离子从星形胶质细胞泄漏到细胞外空间。
