Extracellular potassium activity during epileptogenesis

Abstract

Direct measurements of extracellular potassium concentration ([K +] 0) changes in penicillin epileptogenic foci of cat cortex were made using potassium-sensitive microelectrodes. Interictal EEG events were accompanied by increases in [K +] 0 lasting several seconds. The amplitudes and rise rates of these increases varied with cortical depth, distance from the center of the focus, and the [K +] 0 at which they occurred. During ictal events, [K +] 0 consistently reached 9–10 m m. The patterns of ictal [K +] 0 changes also showed variations with depth in the cortex and distance from the focus. There was an upper limit for [K +] 0 during both interictal and ictal epileptiform activity at about 10 m m. The role of these [K +] 0 changes in modulating neuronal excitability in the epileptogenic focus is discussed. The [K +] 0 level did not appear to be a critical factor in initiation or termination of ictal episodes.