Fast extracellular calcium transients: involvement in epileptic processes.

Improved liquid ion-exchanger microelectrodes made possible the observation of large, rapid decreases in the concentration of extracellular calcium ions during single epileptic spikes. Moreover, in definite cortical layers the decreases regularly started shortly before the onset of each epileptic spike. In view of the prominent role played by extracellular calcium ions in neuronal processes, including transmitter release and membrane excitability, these alterations probably exert a profound influence on the cellular events underlying epileptiform activity.