[Diminution of the extracellular concentration of calcium ions during focal epileptic crisis induced by enanthotoxin in the cat cortex].

OEnanthotoxin applied locally onto the Cat cortex produced a long-lasting epileptic focus. The basic cortical level of extracellular calcium concentration ([Ca2+]e) was decreased before the actual onset of paroxysmal discharges. In the active focus the [Ca2+]e decrease induced by a cortical or a thalamic stimulation was larger than in normal cortex. Maximal decreases were found at a depth of 300 micrometer below cortical surface. It is suggested that at this cortical level calcium conductances are increased by oenanthotoxin. This increase may be one of the mechanisms of onset of epileptic seizures.