Stimulation induced changes in extracellular free calcium in normal cortex and chronic alumina cream foci of cats.

Changes in extracellular [Ca2+]0 (delta Ca) were measured with ion selective microelectrodes in the sensorimotor cortex of cats, surrounding alumina cream lesions and in the contralateral homotopic cortex. The lesions were produced by topical application of alumina cream 6 months-6 years prior to experiments. In normal cortex, stimulus induced reactions of [Ca2+]0 were found to be maximal (up to 0.45 mM) in depths of 200-300 micrometers below the cortical surface. At depths of 600 micrometers and more below the cortical surface, [Ca+2]0 usually rose by up to 0.2 mM above baseline. In the vicinity of the chronic lesion as well as in contralateral cortex [Ca2+]0 fell initially during stimulation in all depths. Close to the lesion delta Ca was as high as 0.8 mM and sites of maximal delta Ca were found to be located deeper in the cortex. About 5 mm from the scar as well as in the contralateral homotopic cortex, maximum delta Ca levels were found in a depth of 200-300 micrometers. It is suggested that Ca2+ dependent mechanisms are involved in epileptogenesis in chronic epileptic foci.