The functional role of the glial network as a draining system for extracellular potassium (spatial buffer) was investigated in rat neocortical brain slices. After electrical stimulation, extracellular space volume decreased in the middle cortical layers and increased in the upper cortical layers, confirming predictions for a spatial buffer. The widening of extracellular space was associated with an increase in extracellular potassium. The data suggested a delayed redistribution of potassium from middle to superficial cortical layers. Interruption of gap junctions abolished the widening of extracellular space. The data show that a multicellular directed network connected by gap junctions participates in maintaining potassium homeostasis in brain. GLIA 29:288–292, 2000. © 2000 Wiley-Liss, Inc.