Role of astrocytes in the clearance of excess extracellular potassium

The development of concepts describing potassium clearance mechanisms in th e mammalian central nervous system in the last 35 years is reviewed. The pa ttern of excess potassium in the extracellular space is discussed as are th e implications of these potassium levels for neuronal excitability. There i s a systematic description of the available evidence for astrocytic involve ment in situ. The three possible astrocytic potassium clearance mechanisms are introduced: spatial buffer mechanism; carrier-operated potassium chlori de uptake as well as channel-operated potassium chloride uptake. The three mechanisms are compared and their compatibility is discussed. Evidence is n ow available showing that at least two of these if not all three mechanisms co-exist and complement each other. Finally, it is concluded that these po tassium movements are not used as a signal system, only as a homeostatic fe edback mechanisms. Such a genuine signal. system involving glial elements e xists - but it is based on calcium waves. (C) 2000 Elsevier Science Ltd. Al l rights reserved.