title: Neocortical microenvironment in patients with intractable epilepsy: potassium and chloride concentrations.
abstract: OBJECTIVE
  The regulation of extracellular ion concentrations plays an important role in neuronal function and epileptogenesis. Despite the many studies into the mechanisms of epileptogenesis in human experimental models, no data are available regarding the fluctuations of extracellular potassium ([K(+)](o)) and chloride ([Cl(-)](o)) concentrations, which could underlie seizure susceptibility in human chronically epileptic tissues in vivo.
  
  
  METHODS
  By using cerebral microdialysis during surgical resection of epileptic foci, the basic [K(+)](o) and [Cl(-)](o) as well as their changes after epicortical electric stimulation were studied in samples of dialysates obtained from 11 patients by ion-selective microelectrodes.
  
  
  RESULTS
  The mean basal values of [K(+)](o) and [Cl(-)](o) in all patients were 3.83 +/- 0.08 mM and 122.9 +/- 2.6 mM, respectively. However, significant differences were observed in the basal levels of both [K(+)](o) and [Cl(-)](o) between different patients. Statistically, no correlation was found between basal [K(+)](o) or [Cl(-)](o) and electrocorticogram (ECoG) spike activity, but in one patient, dramatically lowered baseline [Cl(-)](o) was accompanied by enhanced ECoG spike activity. Application of epicortical electrical stimulation increased [K(+)](o) but not [Cl(-)](o) in all cases. According to the velocity as well as spatial distribution of [K(+)](o) reduction to the prestimulation levels, three different types of responses were observed: slow decline, fast decline, and slow and fast declines at adjacent sites.
  
  
  CONCLUSIONS
  These data may represent abnormalities in ion homeostasis of the epileptic brain.
authors.affiliation: Institut für Physiologie I, Universität Münster, Robert-Koch-Strasse 27a, D-48149 Münster, Germany. gorjial@uni-muenster.de
authors.forename: Ali
authors.initials: A
authors.lastname: Gorji
authors.forename: Nina
authors.initials: N
authors.lastname: Stemmer
authors.forename: Bernhard
authors.initials: B
authors.lastname: Rambeck
authors.forename: Uwe
authors.initials: U
authors.lastname: Jürgens
authors.forename: Theodor
authors.initials: T
authors.lastname: May
authors.forename: Heinz Wolfgang
authors.initials: HW
authors.lastname: Pannek
authors.forename: Friedrich
authors.initials: F
authors.lastname: Behne
authors.forename: Alois
authors.initials: A
authors.lastname: Ebner
authors.forename: Hiedrun
authors.initials: H
authors.lastname: Straub
authors.forename: Erwin-Josef
authors.initials: EJ
authors.lastname: Speckmann
mesh_terms: D000293:Adolescent; D000328:Adult; D000927:Anticonvulsants / Q000627:therapeutic use; D001923:Brain Chemistry; D002712:Chlorides / Q000032:analysis / Q000378:metabolism*; D004351:Drug Resistance; D004558:Electric Stimulation; D004569:Electroencephalography / Q000379:methods / Q000706:statistics & numerical data; D004827:Epilepsy / Q000175:diagnosis* / Q000188:drug therapy / Q000378:metabolism*; D005110:Extracellular Space / Q000737:chemistry / Q000378:metabolism; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D017736:Ion-Selective Electrodes; D008279:Magnetic Resonance Imaging; D008297:Male; D017551:Microdialysis; D008839:Microelectrodes; D008875:Middle Aged; D019579:Neocortex / Q000737:chemistry / Q000378:metabolism* / Q000601:surgery; D011188:Potassium / Q000032:analysis / Q000378:metabolism*; D013702:Temporal Lobe / Q000737:chemistry / Q000378:metabolism / Q000601:surgery; D014018:Tissue Distribution
chemical_list: D000927:Anticonvulsants; D002712:Chlorides; D011188:Potassium